School of Earth Sciences

University of Birmingham


B15 2TT



Department of Geology

University of Manchester

Oxford Road


M13 9PL




There are two main groups of grey-coloured copper sulphosalts (sulphides with arsenic, antimony or bismuth), the fahlerz or tetrahedrite group ranging in composition between tetrahedrite Cu12Sb4S13 and tennantite Cu12As4S13 and the enargite group with enargite and luzonite, both Cu3AsS4, and famatinite Cu3SbS4. These are primary minerals and not the products of secondary processes so are not characteristic of the upper supergene enrichment or gossan zones of orebodies.

Within the tetrahedrite group, a wide range of metals including Ag, Fe, Zn, Cd and Hg can substitute for copper, and these elements, in particular zinc and silver, together with arsenic and antimony may be carried over into any metal smelted from these ores.

Tetrahedrite group minerals are present in many base-metal deposits, hence within the British Isles they are known from many metalliferous occurrences although they are only present in sufficient amounts to be considered potential ores in Devon and Cornwall and in the copper-silver ± mercury deposits of the Munster-Shannon Basin of Ireland. By contrast the enargite minerals have been recorded only rarely in Britain and Ireland and world-wide are best known for their association with epithermal gold deposits.

Amongst the thirty recognised Bronze Age mine sites in the British Isles, fahlerz minerals are present in ore quantities only at Ross Island, Killarney, Ireland where tennantite forms part of a number of mineralogically different, arsenic-bearing, copper assemblages that were exploited during the Early Bronze Age. At Western Mine thin veinlets, comprising complex intergrowths of chalcopyrite-tennantite (with an approximate composition of  (Cu10FeZn)12( As3.8Sb0.2)4S13  accompanied by trace amounts of silver and cobalt phases, cut recrystallised limestones. Coarse-grained chalcopyrite ± arsenopyrite-rich, tennantite-, or bornite-rich ores from the same area, but totally removed in the nineteenth century, may represent a more extensive development of these veinlets. Approximately 100 metres east of the Bronze Age workings at Western Mine are further outcrops of mineralisation at Blue Hole. Here, fine-grained chalcopyrite-pyrite with minor galena and sphalerite pass into finely banded sphalerite-galena accompanied by lesser amounts of pyrite and chalcopyrite. Minor to trace amounts of arsenopyrite and tennantite are present in the Blue Hole ores but  arsenides and sulpharsenides are only of minor importance. Supergene and oxidation zone minerals are poorly developed and so the availability of secondary minerals including arsenates was very limited.

Preliminary evidence from the ongoing archaeological excavations at Ross Island indicates that both tennantite- and arsenopyrite-bearing ores from Western Mine and perhaps some fine-grained, banded, chalcopyrite-pyrite ± sphalerite ± galena ores from Blue Hole were exploited in the Early Bronze Age as copper ores. If this is correct it suggests that fahlerz-bearing ores played a role very early in Bronze Age metallurgy at least once in the British Isles.



Introduction-Orebody characterisation

An understanding of what constituted a copper orebody and copper ore in the Bronze Age and then finding and recognising them are fundamental first steps before any interpretation of Bronze Age metal working practices is possible. It is only after this interpretation that any meaningful provenance studies of the resultant metalwork can be undertaken (Ixer, 1995; 1997; 1999; Ixer and Budd, 1998).


The concepts of an orebody and of ore are sophisticated, indeed both have legal meanings that not only involve geological and mineralogical considerations but also those from mining, economics and sociology. The fundamental difference between a mineral occurrence/mineral association and an ore is not geological but depends on the idea of benefit/profit to an individual/community or ‘society’ and where this benefit may be material, commercial or even intangible. Hence an ore must have all of the following properties –sufficient metal (ore grade) and tonnage, continuity of supply and be amenable to mining and beneficiation at a profit. If one or more of these requirements are missing the material cannot be, by definition, an ore.


Metals are extracted from ores, taken from an orebody. Many orebodies were not formed by a single geological process but by polyphase mineralisation events, often genetically unrelated to each other. This is one reason why few orebodies are simple with a single, uniform ore type but are inhomogeneous that is, the primary ores are zoned. In addition, most ore deposits show a second type of zoning, one that is superimposed on any primary zoning. Characteristically this takes the form of a surficial, friable, limonitic, gossanous zone, rich in metal oxides, hydroxides, carbonates, sulphates, arsenates etc. but poor in sulphides, overlying a supergene enrichment zone containing numerous, mineralogically simple, secondary sulphides. Both these zones overlie the primary ore, which is itself often zoned in terms of metal content (ore grade), mineralogy (mineral species), grain size and mining characteristics.  An orebody, therefore, can comprise any number of mineral associations but it is only those assemblages that were exploited as ore for use in metal production that have significance for archaeometallurgists.


A lack of an appreciation of the difference between ore and mineralised rock specimens has meant that much geochemistry and isotopic work has been done on inappropriate material. This has lead to the so-called ‘Magpie School of Provenancing’ where appearance is given more scientific value than smelting potential, such that run-of-the-mill ores are neglected in favour of high-grade or easy to analyse but atypical mineralogical specimens (Ixer, 1997; 1999). Alongside this, there are misconceptions in the archaeological literature regarding individual mineral associations/ores. This is most noticeable in the identity, chemistry, origin and natural occurrence of the grey copper sulphosalts including the fahlerz and these errors have compromised suggestions regarding the role of fahlerz in Bronze Age metallurgy within the British Isles and elsewhere.


In order to counter these errors, the mineralogy, genesis and occurrence of the fahlerz and enargite groups of minerals are given in some detail emphasising their wide-ranging chemical compositions. This is followed by a description of secondary and primary arsenic-bearing mineral associations within the context of the Bronze Age in the British Isles and finally a more detailed discussion of the fahlerz and other arsenic-bearing ores of the Early Bronze Age mine site at Ross Island, Ireland.


The mineralogy and occurrence of the grey copper sulpharsenides


Fahlerz (or fahlore) is an 'informal' group name for tetrahedrite-tennantite a series of copper sulphosalts (sulphides with As, Sb or Bi); the name is derived from the German word meaning 'pale ores'. The tetrahedrite group of minerals have a cubic structure based on that of sphalerite (ZnS) (Wuensch, 1964) and are so called because crystals take the form of distinctive tetrahedra as shown in figure 1. Tetrahedrite group minerals are economically important, as copper ores and are the world's most important primary source of silver.


Tetrahedrite group mineral chemistry


Tetrahedrite group minerals have the most varied chemistry of any of the sulphides and have been extensively analysed by electron microprobe (Springer, 1969; Charlat and Levy; 1974; Pattrick and Hall, 1983; Johnson et al, 1986). The tetrahedrite structure has sites available for uni- di- and trivalent cations such that the general unit formula is:


and thus a typical formula of a natural tetrahedrite might be Cu10Zn2Sb4S13. The combination of these varied sites in the structure (figure 2) and the formation in a wide range of deposits leads to an enormous range of compositions and a number of 'mini' solid solution series. If all elements found in the group are taken into account, the general formula can be described as:

(Cu,Ag)10(Zn, Fe, Cd, Cu, Mn, Hg)2(As,Sb,Bi)4(S,Se,Te)13

Antimony and arsenic are the common M3+ elements found in the mineral with Sb end-members termed tetrahedrite [1]* (also used as the name for the whole group and often written in the plural) and the As end-members termed tennantite [2], with complete solid solution between them [3]. Bismuth is a rare constituent but has been found in significant concentrations in Bi-rich assemblages such as found in pegmatites [4]. Many tetrahedrites contain only copper [1-4] as the M+ element, although silver can replace up to 4 of the 10 Cu atoms per unit formula [5], rarely up to 7 atoms [6], and very exceptionally more than 7 atoms [7]. Silver-bearing varieties are termed 'argentian tetrahedrite' [4] but those with more than 5 silver atoms of the 10 M+ atoms are termed freibergite [6,7].  There is a very close positive correlation between a high Ag content and a high Sb content due to structural limitations on Ag substitution in As-rich varieties (Johnson and Burnham, 1985; Charnock et al, 1989a).


The commonest M2+ elements in tetrahedrite are Zn and Fe, one or both of these are omnipresent [1-11]; there is a correlation between high Ag and high Fe in tetrahedrites (Pattrick and Hall, 1983). Zinc and iron are replaced to lesser or greater extent by several other elements in relatively restricted occurrences. Mercurian (Hg-bearing) tetrahedrites (8) have been recorded where Hg is found in both Sb- and As-rich varieties. A general positive Hg/Sb correlation was recognised by Charlat and Levy (1974) but locally positive Hg - As correlations occur, such as in the Gortdrum Cu-Hg-As deposit, Ireland. Cadmium, although common in hydrothermal fluids, occurs rarely in tetrahedrites, preferring to substitute into sphalerite, ZnS. The first discovery of Cd-tetrahedrite was as exsolved grains from galena in a low temperature base-metal deposit where up to 11.7 wt% Cd was recorded in silver-rich tetrahedrites (Pattrick, 1978; 1985)[9]. Very rarely, Pb (Bishop et al., 1977; Ixer and Stanley, 1983) [10] and Mn [11] (Burkhart-Baumann, 1984) have been recorded in tetrahedrites. In some tetrahedrites, copper (as Cu+) in excess of 10 atoms per unit formula of M2+ is present, the valence deficiency is compensated for by Fe3+ instead of Fe2+ (Charnock et al., 1989b). Recently, an indium-bearing tennantite has been reported from the Neves Corvo mine in the Iberian Pyrite Belt, Portugal (Pinto et al., 1994).  


Selenium and tellurium only replace sulphur in small amounts but a rare variety of tetrahedrite called goldfieldite contains significant Te4+ which replaces the M3+ elements - the charge imbalance is restored by the omission of the M2+  elements giving an ideal formula of Cu10Te4S13 [13] (Shimizu and Stanley, 1991).


It should be noted that, despite the wide range of metals that can be present in tetrahedrites, lead, nickel and cobalt are very rare or unknown components and hence cannot ‘carry through to the smelted metal’ (Craddock, 1995) if only pure fahlerz is used.


Tetrahedrite group mineral associations


The main occurrence of tetrahedrite group minerals is as primary (hypogene) precipitates from hydrothermal solutions, either in base- or precious-metal sulphide deposits. They vary in abundance from a minor component of ores, such as inclusions exsolved from galena (the cause of much 'argentiferous' galena), to being a major ore mineral. Tetrahedrites can be associated and co-exist with a very, very wide range of minerals including the base-metal sulphides (chalcopyrite, galena and sphalerite), other Cu-Ag sulphosalts, pyrargyrite-proustite (Ag3(As,Sb)S3) and precious metal tellurides (Seal et al.,1990). Tetrahedrite is often found as a replacement of earlier formed sulphides or sulphosalts, due to the reaction of minerals such as sphalerite and chalcopyrite with later As and Sb (Cu)-bearing hydrothermal fluids. The composition of the tetrahedrite often reflects the chemistry of the associated sulphide minerals. Where it forms as a replacement of existing phases, the chemistry of those phases is inherited (e.g. tennantite after arsenopyrite (FeAsS) or freibergite after miargyrite (AgSbS2); it is under such conditions that 'exotic' compositions can form. However, it should be stressed that the replacement of earlier minerals by tetrahedrite is part of the primary mineralisation and not part of the later processes of supergene enrichment or weathering, as widely reported in the archaeological literature (Craddock, 1995). Indeed, during weathering, tetrahedrite group minerals breakdown to secondary sulphides such as chalcocite, chalcopyrite, (as found in sulphide-rich supergene 'blankets'), covelline (CuS), acanthite (Ag2S) and Zn-, As- and Fe-hydroxyoxides and carbonates and arsenates like olivenite (Cu2AsO4.OH).


Tetrahedrite group minerals- occurrence and formation



Tetrahedrite is stable over very wide range of ore-forming conditions and is therefore found in almost all types of hydrothermal sulphide deposits throughout the world. Tetrahedrite group minerals are usually precipitated from acidic, saline mineralising fluids in the temperature range 200 to 400oC and over a wide range of redox conditions. They are common accessory minerals in volcanogenic massive sulphide (VMS) deposits, especially in the black ore (sphalerite-galena-pyrite) of Kuroko deposits (such as at Avoca, Ireland and Parys Mountain, Wales), but also in their chalcopyrite-rich yellow ores and in Cyprus-type deposits. Tetrahedrite minerals are recorded in present day active hydrothermal vent systems found at mid-oceanic ridges, forming within the black smokers chimney structures (Meecham, 1990). Sedimentary exhalative (SedEx) and associated deposits contain significant tetrahedrite, as for example, at Mt Isa, Queensland (Riley, 1974) whilst the similar Irish base-metal deposits; Tynagh and Abbeytown, have significant tennantite (figure 3), with silver-rich pods in Silvermines containing minerals of the freibergite-argentotennantite series (Zakrzewski,1989). Argentian tetrahedrite and freibergite also occur in the enigmatic Co-As assemblages in Cobalt-Gondwana type ores, which are possibly associated with basic igneous activity. The Tsumeb breccia pipe in Namibia contains abundant tennantite.


Tetrahedrite group minerals are ubiquitous in polymetallic veins and skarns formed by hydrothermal activity associated with high level intermediate or acid igneous rocks - especially in the meso- and epithermal deposits of the western Americas related to Andean (the Cordilleran Veins) and Laramide orogenesis. Mineralisation related to hydrothermal convection associated with igneous intrusive (I-type) activity often contains tetrahedrite group minerals. Copper porphyry deposits, the main source of the world's copper, have chalcopyrite as the main Cu-ore but many contain tetrahedrite minerals in significant concentrations as at Butte, Montana; Bingham, Utah and Chuquicamata, Chile. Mineralisation is often associated with evolved S-type granites and tetrahedrite group minerals are common components of spatially related Cu-rich veins. Examples include those formed close to the Variscan granites of Europe; in the Bohemian Massif (Czech Republic-Slovakia) at PéÍbram and Kutn« Hora (where mercurian tetrahedrite is common), and the sulphide-rich veins of the Cornubian tin-copper province of Southwest England.


In addition to the localities already mentioned, tetrahedrite is found widely in sulphide mineralisation of the British Isles although, apart from the Irish deposits and in Cornubia, it is never abundant. There are many occurrences in the granite-related mineralisation of the Caledonides of Scotland (the Lagalochan and Tomnadashan Porphyry Copper Deposits, figure 4), the Lake District and Ireland. One group of deposits world-wide, in which tetrahedrites are rare, are the Mississippi-Valley type deposits because fluid temperatures are often too low to carry copper. However, in deposits hosted by the Carboniferous limestones of the Pennines and Mendips (the F-Ba-Pb deposits), tetrahedrite is present in microscopic amounts, most notably in early high temperature assemblages (Ixer, 1986). Tetrahedrite group minerals also occur in copper veins hosted by Triassic carbonates at Clevedon, Avon (Ixer et al., 1993).


Large scale zoning of As/Sb in tetrahedrites has been noted from several deposits and usually As-rich varieties precede Sb-rich varieties (Johnson et al., 1986; Wu and Petersen, 1977). At Bingham, Utah, the zoning is from As to Sb plus Ag rich varieties; whereas in Kuroko deposits, tennantite is more common in the lower, yellow ores with (silver-bearing) tetrahedrite in the upper, black ores. Similar zoning sequences can occur on the micro-scale, with major changes in chemistry taking place in individual grains over a few microns. Hence fahlerz taken from different places within the same orebody may show quite disparate compositions.




Enargite group


Enargite, Cu3AsS4 is also a grey-coloured copper sulphosalt. It has an orthorhombic sphalerite-based structure and limited As-Sb solid solution (up to a maximum of 10 wt% Sb).  Luzonite, is the low temperature tetragonal dimorph of enargite, which in contrast, has a complete solid solution with an antimony end-member, famatinite, Cu3SbS4. Famatinite (synonymous with stibioluzonite) and intermediate members of the series [Cu3(As,Sb)S4] are stable over a wider temperature range than luzonite.   In the literature, enargite is very often reported where the term enargite group would be more appropriate (Mihaly and Buseck, 1993; Clark, 1993; Feiss, 1974).


As with tetrahedrite, enargite is a primary precipitate from hydrothermal solutions. Although more restricted in occurrence than tetrahedrite it is found in similar assemblages in copper-rich ores and the two minerals can be intergrown. The classic occurrence of enargite group minerals is in 'high sulphidation' (or 'acid sulphate') gold vein deposits, precipitated from high temperature (300-400oC), very acidic, hydrothermal fluids, typically associated with high level intrusions, subvolcanic igneous activity, and collapsed calderas (Perello, 1994). These deposits have sometimes been called 'enargite-type' as the mineral is one of their characteristic features and are found the world over. The best examples are in the Circum-Pacific volcanic ring; such as in the Philippines (including Luzon), Indonesia, Japan, the Andean and Rocky Mountain vein deposits, including those in the San Juan Mountains of Colorado.


In porphyry copper deposits, enargite forms late in the main hydrothermal mineralising episode within a high sulphidation zone effected by acidic fluids which produced a retrograde assemblage showing for example the replacement of pyrite and bornite by enargite and tennantite (Guilbert and Park, 1985).  Enargite is found in many other deposit types, but is not as widespread as tetrahedrite, hence it has rarely been reported from the British Isles. However, enargite group minerals have been described from a low temperature deposit at Clevedon, Bristol where typical intermediate luzonite-famatinite occur [15] (Ixer et al., 1993); the North Pennines (Vaughan and Ixer, 1980; Ixer and Stanley, 1998); the South Pennines (Cooper, 1995) and the copper deposit of Alderley Edge (Ixer and Budd, 1998). In all of these occurrences the minerals are present in microscopic amounts and cannot be considered as ore.




Copper-arsenic secondary mineral assemblages 


Unlike the restricted number of copper arsenic sulphides, there are quite a number of copper arsenates and even more copper-bearing lead, uranium, calcium, rare earth element, iron or zinc arsenates. However, ‘most are so rare that they are seldom seen’ (Blackburn and Dennen, 1994). Typically these copper-arsenic-bearing secondary minerals are brightly coloured and found in minor to trace amounts in the upper oxidised zones (gossans) of arsenical copper deposits, or even on mine spoil, having formed as part of their post-mining oxidation by local groundwaters.


The rarity, bright colours and unusual crystal habits of these arsenates are attractive to mineral collectors (especially those who specialise in micromounts) so that the minerals have been reported from a large number of mineral localities including many in the British Isles. In particular, a wide range of minerals are known from mine sites in parts of the Caldbeck Fells in the English Lake District (Cooper and Stanley, 1990), locally within the Central Wales Orefield (Rust and Mason, 1994) or even from individual mines like Alderley Edge in Cheshire (Braithwaite, 1994). However, the greatest concentration of copper and copper-bearing arsenates is reported from Devon and Cornwall (Embrey and Symes, 1987), where locally, as for example at Wheal Gorland in the St Day district of central Cornwall, the mine dumps are well known for their arsenate assemblages (C. Stanley, pers.comm.).


 Supergene oxidation of tennantite-tetrahedrite or mixed copper-iron-sulphur-arsenic ores (for example chalcopyrite-arsenopyrite) can lead to the formation of green copper arsenates including olivenite (Cu2AsO4(OH)), clinoclase (Cu3(AsO4)(OH)3), cornwallite (Cu5(AsO4)2(OH)4.H2O)  and cornubite(Cu5(AsO4)2(OH)4)  and liroconite (Cu2Al(AsO4)(OH)4.4H2O) alongside the more common minerals arsenolite (As2O3) and scorodite (FeAsO4.2H2O). These copper arsenates have no present day economic value other than as mineralogical specimens. However, some workers, notably Charles (1967, 1994), have suggested that within the British Isles green arsenates (originally mistaken for malachite) became important Early Bronze Age copper ores capable of producing arsenical copper (Group 1) metal without any by-product slag.  Characteristically, metal slags are absent from British and Irish Bronze Age mine sites, which is difficult to explain as smelting of sulphides ± arsenides or fahlerz-bearing ores should leave a residual slag (Craddock, 1995). It was to explain this absence that Charles, (1967) first proposed the use of copper arsenates as ore. 

More recently Pollard et al (1991) and Budd et al (1992) employing theoretical and experimental chemistry have suggested that arsenical copper was smelted from secondary copper minerals (malachite, azurite) mixed with copper arsenates in an essentially non-slagging process. Although it may be possible to produce arsenical copper in the laboratory from copper arsenates this does not make them an ore. Minerals must be present, not just in traces but in sufficient amounts to be exploitable and this does not appear to be true for copper arsenates in the British Isles (Ixer and Budd, 1998).


 The distribution of fahlerz and other arsenic-bearing mineral assemblages within the Bronze Age mine sites of the British Isles


Earlier speculations that Bronze Age mine sites in the British Isles were fahlerz-bearing (Mount Gabriel, Jackson 1968, 1980) or contained arsenical ores (Alderley Edge, Pollard et al., 1991; Budd et al., 1992) have been shown to be incorrect. Ixer and Budd (1998), in a review of the mineralogy of the mineral associations and copper ores from the major prehistoric mines of Britain and Ireland, have shown that some are free of fahlerz (Mt. Gabriel and Cwmystwyth) and in others that fahlerz is only present in microscopic amounts (Alderley Edge and the Great Orme). Elsewhere, where it is present it is restricted to ores that could not be beneficiated (the process of physically separating wanted ore minerals from each other and from unwanted gangue) using Bronze Age technology (Parys Mountain).


 Similarly, despite the statement of Craddock, (1995) that ‘olivenite is not uncommon in the upper oxidised zones of copper deposits’, for most ore deposits in the British Isles and for all known Bronze Age mine sites, arsenates are mineralogical curiosities (Ixer, 1995; Ixer and Budd, 1998) without sufficient tonnage (i.e. kilograms to tens of kilograms) to be treated as copper ore.  In particular, contrary to the suggestion of Pollard et al (1991), the copper ores of Alderley Edge have insufficient amounts of arsenates (or arsenides or sulpharsenides) to produce arsenical copper (Ixer and Budd, 1998). It is only in the unglaciated, tin-copper metallogenic province of Cornubia (Devon and Cornwall) with its abundance of arsenopyrite- and fahlerz-bearing, primary copper ores and their secondary gossans (Alderton, 1993) that arsenates may have been of importance, but even here their distribution is restricted and uneven.


Ross Island in Munster, western Ireland stands alone as a known Bronze Age mine site with sufficient quantities of arsenic-bearing minerals amongst its ores/potential ores to make the production of Group I metal possible.






The geology and mineralogy of arsenic-bearing assemblages from Ross Island


O'Brien (1995 and this volume) has described the archaeology and mining activity at Ross Island, Killarney, Co. Kerry and, in particular, the Bronze Age mine and work camp at the Western Mine area. This mine site is potentially the most important for our understanding of Early Bronze Age mining and metallurgy within the British Isles, and even for Northwest Europe. It is unique amongst the thirty or so known Bronze Age mines in the British Isles for two reasons:


 firstly, mining activity has been securely dated to 2500-2000 BC, beginning in the Final Neolithic/Copper Age and continuing through all the time that arsenical copper (Group 1/Group A metal) was being produced and in circulation (O'Brien 1995).  These are the earliest dates recorded for any British or Irish mine site.


 Secondly, only Ross Island had sufficient quantities of chalcopyrite-tennantite or chalcopyrite ± arsenopyrite ± pyrite that these can be considered to be copper ores, and so it is alone in having the potential to produce arsenical copper or copper metal with significant amounts of arsenic. 


Preliminary descriptions of the geology and genesis of the mineralisation at Ross Island - Muckross are given by Weaver (1838) and Ixer and Patrick (1995) whilst the mineralisation as Bronze Age ore has been discussed by Ixer et al. (1995) and Ixer and Budd (1998). Tennantite and trace amounts of enargite-bearing copper ores at the Ross Island site are part of a discontinuous zone of mineralisation stretching south-eastwards from Ross Island (Western Mine and Blue Hole) to Crow Island to Muckross Mine and beyond. Historical mining has taken place along a strike length of two kilometres. At Ross Island, stratabound Cu-Pb-Zn-As plus minor silver and cobalt mineralisation is present as sulphides, arsenides and sulpharsenides. These are intermittently developed in 'beds' up to 3 metre thick within a 20 metre thick, highly brecciated, dolomitised, partially silicified, and intensely recrystallised Lower Carboniferous limestones, close to the present day land surface (Weaver, 1838; Ixer and Pattrick, 1995).  The mineralisation is epigenetic and displays a number of different styles and mineral associations (ores).  Amongst the most important are: -


1.         Thin, cross-cutting veinlets or disseminations in limestones- these are found in situ in the Western Mine. The veinlets comprise complex intergrowths of chalcopyrite (CuFeS2) - silver-poor tennantite ((Cu10FeZn)12(As3.8Sb0.2)4S13) with up to 0.3 wt % silver, together with trace amounts of nickeliferous cobaltite ((CoNi)AsS), molybdenite (MoS2) and pyrite (FeS2), plus a little secondary stromeyerite (AgCuS) and native silver, all within a calcite gangue (Ixer and Pattrick 1995).


2.         Richer, coarse-grained copper ores were mined during the nineteenth century from the Western Mine area, although there is almost no trace of them today and nothing is found in situ.  Weaver (1838) gives the only account of these ores at Ross Island (and at Muckross) before their exhaustion and perhaps total removal in the 1820s.  In particular he lists three copper ores with metal contents of 10 to >15% Cu; these are "rich, grey copper sulphuret" (fahlerz-rich ore); "purple sulphuret" (bornite-rich ore) and "yellow sulphuret" (chalcopyrite-rich ore).  As these ore types are distinguished from “copper pyrites,” a lower grade, chalcopyrite-pyrite ore, these three rich ores are here interpreted to mean coarse-grained, non-banded, massive sulphides.  Weaver noted that these rich copper ores were common in the pre-1820 spoil and suggested their collection and removal - the extreme paucity of this material in the post-1820 spoil (only one or two examples of each have been found) suggests that his advice was acted upon. Despite their rarity, examples of all three of Weaver's ore types have been collected and examined.  They form a continuum from tennantite plus minor chalcopyrite and trace amounts of molybdenite, pyrite, cobaltite and stromeyerite ('grey sulphuret ore') to chalcopyrite or chalcopyrite-arsenopyrite plus minor to trace amounts of tennantite, galena and molybdenite ('yellow sulphuret ore'). They also share the same mineralogy, mineral textures and paragenesis as the in situ chalcopyrite-tennantite veinlets from the Western Mine area. The third ore type 'purple sulphuret' is a coarse-grained mixture of bornite (Cu5FeS4) - 'idaite' (a fine-grained crystallographic intergrowth of bornite-chalcopyrite-covelline) -chalcopyrite plus minor amounts of molybdenite, pyrite and tennantite; the extensive replacement of the iron-copper phases in this ore type by spionkopite (Cu39S28) may be a post-mining, weathering phenomenon. 


3.        Blue Hole, which is approximately 100 metres from the Bronze Age workings at Western Mine, may also have been the site of Bronze Age mining activity (O'Brien 1995). Here the mineralisation comprises fine-grained, banded, massive sulphides infilling void spaces within karstic surfaces (A. Bowden pers.comm.). However, the detailed field relations between the mineralisation and its host rocks have yet to be interpreted and so the exact style of mineralisation at Blue Hole remains unclear. The sulphides vary from yellow-coloured chalcopyrite-pyrite with minor galena and sphalerite and trace amounts of arsenopyrite (FeAsS) and tennantite to finely banded, dark grey-black- coloured ores comprising sphalerite (ZnS) and galena (PbS) with lesser amounts of pyrite, chalcopyrite and trace amounts of arsenopyrite and tennantite.


4.       The historical account of Weaver (1838), plus inspection and sampling of six drill cores, as well as outcrop show most of the mineralisation to be unaltered sulphides/sulphosalts with only a minor development of a secondary enrichment zone or a gossan.  The absence of any gossan is especially marked in the Western Mine area and is explained by the lack of pyrite, for it is the initial oxidation of pyrite that begins the process leading to gossan formation.

            However, a wide range of secondary minerals have been recorded from Ross Island including malachite, azurite, cuprite and native copper (Weaver, 1838); serpierite Ca(CuZn)4(SO4)2(OH)6.3H2O from Blue Hole (Russell, 1927), smithsonite ZnCO3, cerussite PbCO3, brochantite Cu4(SO4)(OH)6 and olivenite Cu2(AsO4)(OH) (confirmed by X ray diffraction) and hydrozincite Zn5(CO3)2(OH)6 and erythrite Co3(AsO4)2.8H2O (Ryback and Moreton, 1991).  Most occur in microscopic amounts on oxidised spoil samples and very commonly on mineralised material recovered from the excavations. Ryback and Moreton, (1993) and Moreton et al. (in press) (who have recorded an even greater list of secondary minerals from Muckross Mine including nickel, iron, calcium and mixed (Co,Ni,Mg,Ca,Fe) arsenates) state that these arsenates formed during post-mining oxidation of mine waste and that most are exceedingly rare; these statements apply equally well to Ross Island.




   Mineralisation at Ross Island as Bronze Age Ore


Petrographic investigations of material taken from nineteenth century spoil, drill core and the archaeological excavation clearly demonstrate that there are a number of distinctive mineral associations present at Ross Island.  They further show that the mineralisation at the Western Mine area (massive chalcopyrite-tennantite ± bornite) is different from the bedded sulphides (chalcopyrite-pyrite-sphalerite-galena) found in the Blue Hole area. However, for these mineral associations to become ore, they have to fulfil the criteria described earlier. That is, they need to be readily mineable, to have sufficient tonnage and metal grade, and to be amenable to beneficiation in order to produce a clean (free of harmful or unwanted impurities), metal-rich concentrate that can be smelted easily. 


All the mineralisation lies close to the surface lying at a maximum depth of less than twenty metres and is hosted within the 'blue limestone' (Colleen Baun Limestone Member) a hard, heavily fractured but recrystallised, bioclastic limestone mineable by firesetting (O'Brien 1995).  Archaeological and historical evidence shows that the primary mineral assemblages at Ross Island had a sufficient tonnage to sustain both Bronze Age and Early Christian Age metal mining and still provide a final 3000 tons of dressed copper ore in the 1820s.  


Thin chalcopyrite-tennantite veinlets found in situ in the Western Mine area constitute the most abundant mineralised material recovered during the excavations of the work camp where they are present as comminuted fragments (O'Brien 1995).  The ore-grade of this mineralisation is variable but hand cobbing of thicker veinlets (> 1 centimetre in width) and of bunches of ore could produce a mixed chalcopyrite-tennantite copper concentrate with more than 10% copper metal, but also carrying major iron and arsenic and trace amounts of antimony, silver and cobalt.


The copper ores described by Weaver, which may have underlain the chalcopyrite-tennantite veinlets (Weaver 1838), or were richer, coarse-grained versions of them (Ixer and Pattrick, 1995), have metal grades of >10% Cu. These, therefore, should be regarded as potential Bronze Age ores - indeed examples of all three have been recovered during the excavation of the work camp area. They would not require beneficiation but only crushing before being smelted. Any copper metal produced from them could contain the following impurities iron (present in chalcopyrite, bornite, pyrite and arsenopyrite), plus variable but significant amounts of arsenic (present in tennantite, arsenopyrite and cobaltite) and trace amounts of molybdenum (molybdenite), silver (tennantite and stromeyerite), cobalt and nickel (cobaltite). 


It is difficult to determine if the fine-grained, chalcopyrite-pyrite-rich, massive sulphides from the Blue Hole area were Bronze Age ores but the presence of two caches, one up to 2.7 kilograms in weight, of this material within the work camp suggest that, at least, they were regarded with interest.  Ten samples taken from the larger cache are between 2.5 to 5 centimetres in diameter (mainly 3 to 4 centimetres) with an orange-brown limonitic crust up to five millimetres thick. When broken they range in colour from yellow (chalcopyrite) to dull yellows (mixed chalcopyrite-pyrite) and most show visible galena.  They share a very uniform petrography with the relative abundance of the minerals being chalcopyrite > pyrite > sphalerite > galena >> tennantite > arsenopyrite.  All show complex intergrowths between the minerals and some comprise alternating chalcopyrite- and pyrite-rich bands and galena-rich areas.  Four samples from the other cache are very similar to those of the first cache but a little coarser grained. The grain size and complex nature of the intergrowths between the minerals means that beneficiation would be impossible so that any copper concentrate would carry iron, zinc, lead and arsenic as major impurities. In neither cache were there examples of the fine-grained, galena-sphalerite-rich sulphides present at Blue Hole nor the coarse-grained, tennantite-chalcopyrite ores from the Western Mine area.


 The fine-grained, sphalerite-galena-rich sulphides from Blue Hole cannot be considered to be Bronze Age copper ore, the copper content is low (<2%), the grain size too fine and the mineral intergrowths too complex for a copper concentrate to be produced by any physical means.  Indeed these sulphides were unsaleable in the 1820s, as were the very similar fine-grained, fahlerz-bearing, lead-zinc ores from Parys Mountain, Wales ('bluestone ore') at the end of the same century.  Only a single small piece of sphalerite-galena ore has been recovered from the excavations of the Bronze Age work camp at Ross Island.


Weaver noted the presence of the secondary minerals malachite, azurite and cuprite plus minor amounts of native copper but stated they occur 'much more rarely' and were restricted to a small part of the mine.  Copper arsenates are only present in ‘academic’ amounts and as at Muckross Mine, they may be post-mining in origin (Moreton et al. in press). Hence the amount of copper arsenates compared to fahlerz- or arsenopyrite-bearing ore at Ross Island was trivial and so they are not considered to be ore.


Although excavations up to September 1995 have revealed much Early Christian Age slag, neither Bronze Age copper metal nor slag have been recovered from a securely dated prehistoric context.  A single sample, however, which was initially identified as a vuggy, limonitic gossan but now interpreted as partially roasted ore may give a clue to at least one of the ores used by the Beaker People.  The sample (find number 1242) comprises a mixture of yellow copper-iron sulphide (some of which corresponds in composition to cubanite (CuFe2S3) plus minor amounts of a white iron arsenide close to lØllingite (FeAs2) plus cellular organic matter (wood/charcoal).  Very minor amounts of neomorphic albite and magnetite, itself enclosing traces of copper metal, line the circular walls of the vughs, which are infilled by coarse-grained, post-Bronze Age, secondary cerussite and minor olivenite.  The copper-iron sulphides and iron arsenides are heavily altered to limonite.


Cubanite, lØllingite, magnetite and albite have not been recognised from any of the ore mineral assemblages from Ross Island nor would they be natural alteration products from these ores.  Although cubanite and lØllingite are unlikely results of sulphide-arsenide roasting (T.Rehren pers.comm.) the chaotic mixture of organic matter and ore minerals, the presence of circular vughs (gas bubbles?) and magnetite suggest that specimen 1242 represents a poorly roasted sulphide-arsenide ore. The exact nature of this ore is speculative but a very few fragments of a coarse-grained chalcopyrite-arsenopyrite-rich ore akin to Weaver’s ‘yellow sulphuret ore’ have been recovered during the excavations and may represent the pre-roasting charge.




 Despite the rarity and geographical restriction within the British Isles of fahlerz in sufficient quantities that it could constitute an ore, the data from Ross Island provide evidence that fahlerz did play a significant and early role in Early Bronze Age metallurgy at least once, in Munster. Although the evidence is preliminary it also seems likely that a number of different ore types were being exploited in Ireland during the Early Bronze Age including chalcopyrite-tennantite, chalcopyrite-arsenopyrite and fine-grained, mixed, chalcopyrite-pyrite ± base-metal sulphides. An assessment of the importance of each ore type will only be possible after the relative amounts of ores types (as found in the work camp) have been quantified together with the integration of the post-1995 excavation material. This is currently being studied and includes rare metallurgical residues found in association with Beaker period pit furnaces in the work camp location. Notable amongst these finds are a small number of roasted and altered ore and a metal droplet (O’Brien pers. comm.)


The present work broadly supports O’Brien (1995). He, in a thoughtful and thought provoking contribution, states that at Ross Island, the oldest known copper mine in northwest Europe, people were mining and processing primary fahlerz-bearing ores rather than secondary copper ores to supply Group I (As-Sb-Ag-bearing) metal from 2500-2000 BC, namely until early tin-bronze times.  He further suggests that data from Ross Island strengthen the ideas of Case (1966) and Northover (1980, 1982) that Munster (especially counties Cork and Kerry) was the main source of early copper in Ireland and Britain.  Ixer and Budd (1998) concur but, partially based on the presence of the two caches of fine-grained, chalcopyrite-pyrite ± galena nodules, propose that sulphide ores from Blue Hole may have been processed together with or alongside fahlerz-bearing ores from the Western Mine area.  They also note that all the mineral associations from Ross Island are antimony- and silver-poor (reflecting tennantite rather than tetrahedrite as the main copper sulpharsenide) so that Group I metal with its characteristic As, Sb, Ag trace element impurity pattern, cannot have been made from Ross Island ore alone. This contrasts with O'Brien who comments on the uniformity of Group I metal and wonders if Ross Island were the sole provider of Group I metal to Ireland before urging caution because of the presence in Munster of other fahlerz-bearing mineral assemblages notably Ballycummisk near Mt Gabriel (Ixer, 1990) and Ardtully in the Kenmare Valley as well as arsenopyrite-bearing ores from Dhurode (Ni Wen et al. 1991).


Elsewhere in the British Isles, Bronze Age people could have exploited arsenic-bearing ores from within the copper-tin-arsenic mineral province of Cornubia but, as is well known, there are no recognised Bronze Age mine sites from southwest England.   In addition the widespread presence of primary fahlerz-bearing and chalcopyrite-arsenopyrite-rich ores (plus, perhaps, local concentrations of secondary copper arsenates) makes it impossible to determine what sort of ore, if any, was being exploited. It is worth noting, however, that the evidence from Ross Island would indicate that both fahlerz-rich and chalcopyrite-arsenopyrite primary ore types were of interest to Bronze Age metallurgists, so reinforcing Cornubia as an important potential orefield.


Indeed, mineral deposits from Cornubia and especially Cornwall west of the small city of Truro, include native copper from the Lizard Peninsula, hardrock sources of chalcopyrite-arsenopyrite/fahlerz ± copper arsenates and chalcopyrite-cassiterite ores from numerous coastal and inland exposures plus placer cassiterite from streams.  These localities could have supplied metal for the British Isles from the inception of the Copper Age well into tin-bronze times. Although the combined absence of evidence for early mining, and the negligible amounts of Copper Age metalwork from Cornubia, will continue to be important stumbling blocks to our understanding of Bronze Age mining and metallurgy in mainland Britain, current investigations at Ross Island are ensuring that this is no longer true for the British Isles.




The Ross Island mineralisation study is part of an inter-disciplinary investigation undertaken by University College, Galway in collaboration with other bodies. The Irish Government through the Royal Irish Academy funded the ore analyses. Paul Budd is thanked for stimulating discussions and Paul Craddock for his patience.




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Table 1. Representative electronprobe microanalyses of fahlerz, in wt% and calculated to unit formula using S=13.






















































































































































































































[1] Cu9.95Zn1.86Sb3.92S13 (Tetrahedrite, Siegenland; Springer, 1969)

[2] Cu10.27Ag0.01Zn0.39Fe1.57As3.94Sb0.03S13 (Tennantite, Casapalca, Peru; Wu and Petersen, 1977)

[3] Cu9.90Ag0.08Zn1.19Fe0.81Cd0.01As1.66Sb2.54Bi0.02S13.00 (Tetrahedrite-tennantite, Tomnadashan, Scotland; Pattrick, 1984)

[4]Cu10.1Ag0.1Zn1.6Fe0.6As2.5Bi1.6S13 (Bismuthian tennantite, Manualde, Portugal; Oen and Kiefe, 1976)

[5] Cu9.4Ag1.4Zn0.6Fe1.5As0.5Sb3.9S13 (Argentian tetrahedrite, Coeur d'Alene, Idaho; Knowles, 1987)

[6] Cu3.39Ag5.82Zn0.32Fe1.29As0.08Sb4.14S13 (Freibergite, Mt Isa, Queensland; Riley, 1974,)

[7] Cu0.78Ag9.23Zn0.25Fe1.92Sb4.04S13 (Freibergite, Janggun, Korea; Imai and Lee, 1980)

[8] Cu6.47Ag3.02Zn0.18Hg1.76As0.72Sb3.33S13 (Mercurian tetrahedrite, Chiprovtsi, Bulgaria; Atanasov, 1975,)

[9] Cu8.90Ag1.14Zn0.02Fe0.11Cd1.94Pb0.02As0.28Sb4.2Bi0.01S13 (Cadmium tetrahedrite, Tyndrum, Scotland; Pattrick, 1985)

[10] Cu9.6Ag0.4Zn0.5Fe0..4Pb0.6Sb2.6As1.4S13  (Plumbian tennantite, Sark, Channel Is; Bishop et al., 1977).

[11] Cu11.1Fe0.5Mn1.5As3.9Sb0.3S13 (Manganiferous tetrahedrite, Quiruvilca, Peru; Burkhart-Baumann, 1984)

[12] Cu12.02As1.73Sb0.17Te2.14S13 (Goldfieldite, Butte, Montana; Springer, 1969)

[13] Cu10.7Ag1.1Sb3.8S13 (M2+ deficient tetrahedrite, Ilímaussaq, Greenland; Karup-Møller, 1974)

[14] Cu3.06Fe0.03Cd0.01As0.64Sb0.37S4  (Enargite (Luzonite-famatinite), Clevedon; Bristol; Ixer et al., 1993)


Figure and Plate Captions


Figure 1.  The structure of tetrahedrite group minerals. This figure shows the structure (molecular model) of a tetrahedrite and demonstrates the coordination environment of the atoms. This example is of a tetrahedrite with a chemical formula of Cu10Cd2Sb4S13. The copper occurs in two sites, a four-fold coordinated site (CuIV) and a three-fold coordinated site (CuIII). The Me2+ (in this case Cd) replaces two of the CuIV atoms while Ag preferentially replaces the CuIII atoms. The Me3+ element (Sb) is in three-fold coordination adjacent to a ‘hole’ in the structure. The S atoms are also in two sites, one site (the SIV site) has four-fold S atoms bonded to the CuIV atoms, and another site in which the six-fold S atoms (the SVI) are bonded to the CuIII atoms. (From Pattrick et al., (1993) and after Pauling and Neumann (1934).

Colour Plate 1. Tennantite from veins at Casapalca, Peru. The classic tetrahedra that give the mineral group its name can be seen, growing from massive tennantite. Specimen size 8cms across.


Colour Plate 2.  Complex intergrowths of tennantite (green-grey, bottom left) – galena (white) – chalcopyrite (deep yellow) – sphalerite (light grey, top right).  Rhombic crystals of dolomite (dark grey, centre) are enclosed in the mixed sulphides.  Fine- grained ores like this are very difficult to beneficiate using physical methods.  Tynagh, Ireland.  Field of view 0.7mm. Reflected Light, plane polarised.


Colour Plate 3. Tetrahedrite-pyrite-chalcopyrite from Tomnadashan, Scotland.  Pyrite, (very pale yellow, bottom right) is partially replaced along its cleavage planes by chalcopyrite (deep yellow).  Tetrahedrite (green-grey, left) locally has totally replaced pyrite.  The ore minerals are in a calcite gangue (dark greys).  Field of view 1.3mm.  Reflected Light, plane polarised.




* The numbers in brackets refer to analyses in table 1.

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