Precious and base metal geochemistry and mineralogy of the Grasvally Norite-Pyroxenite-Anorthosite (GNPA) member, northern Bushveld Complex, South Africa : implications for a multistage emplacement

The Grasvally Norite-Pyroxenite-Anorthosite (GNPA) member within the northern limb of the Bushveld Complex is a mineralized, layered package of mafic cumulates developed to the south of the town of Mokopane, at a similar stratigraphic position to the Platreef. The concentration of platinum-group elements (PGE) in base metal sulfides (BMS) has been determined by laser ablation inductively coupled plasma-mass spectrometry. These data, coupled with whole-rock PGE concentrations and a detailed account of the platinum-group mineralogy (PGM), provide an insight into the distribution of PGE and chalcophile elements within the GNPA member, during both primary magmatic and secondary hydrothermal alteration processes. Within the most unaltered sulfides (containing pyrrhotite, pentlandite, and chalcopyrite only), the majority of IPGE, Rh, and some Pd occur in solid solution within pyrrhotite and pentlandite, with an associated Pt-As and Pd-Bi-Te dominated PGM assemblage. These observations in conjunction with the presence of good correlations between all bulk PGE and base metals throughout the GNPA member indicate the presence and subsequent fractionation of a single PGE-rich sulfide liquid, which has not been significantly altered. In places, the primary sulfides have been replaced to varying degrees by a low-temperature assemblage of pyrite, millerite, and chalcopyrite. These sulfides are associated with a PGM assemblage characterized by the presence of Pd antimonides and Pd arsenides, which are indicative of hydrothermal assemblages. The presence of appreciable quantities of IPGE, Pd and Rh within pyrite, and, to a lesser, extent millerite suggests these phases directly inherited PGE contents from the pyrrhotite and pentlandite that they replaced. The replacement of both the sulfides and PGM occurred in situ, thus preserving the originally strong spatial association between PGM and BMS, but altering the mineralogy. Precious metal geochemistry indicates that fluid redistribution of PGE is minimal with only Pd, Au, and Cu being partially remobilized and decoupled from BMS. This is also indicated by the lower concentrations of Pd evident in both pyrite and millerite compared with the pentlandite being replaced. The observations that the GNPA member was mineralized prior to intrusion of the Main Zone and that there was no local footwall control over the development of sulfide mineralization are inconsistent with genetic models involving the in situ development of a sulfide liquid through either depletion of an overlying magma column or in situ contamination of crustal S. We therefore believe that our observations are more compatible with a multistage emplacement model, where preformed PGE-rich sulfides were emplaced into the GNPA member. Such a model explains the development and distribution of a single sulfide liquid throughout the entire 400-800 m thick succession. It is therefore envisaged that the GNPA member formed in a similar manner to its nearest analogue the Platreef. Notable differences however in PGE tenors indicate that the ore-forming process may have differed slightly within the staging chambers that supplied the Platreef and GNPA member

Magmatic sulfide ore deposits

Magmatic sulfide ore deposits are products of natural smelting: concentration of elements from silicate magmas (slags) by immiscible sulfide liquid (matte). Deposits occupy a spectrum from accumulated pools of matte within small igneous intrusions or lava flows, forming orebodies mined primarily for Ni and Cu, to stratiform layers of weakly disseminated sulfides, mined for platinum group elements, within large mafic-ultramafic intrusions. One of the world’s most valuable deposits, the Platreef in the Bushveld Complex in South Africa, has aspects of both of these end members. Natural matte compositions vary widely between and within deposits, controlled largely by the relative volumes of matte and slag that interact with one another

Geochemistry and mineralogy of platinum group element mineralization in the river valley intrusion, Ontario, Canada : A model for early-stage sulfur saturation and multistage emplacement and the implications for "contact-type" Ni-Cu-PGE sulfide mineralization

The River Valley Intrusion (RVI) within the ~2.48 Ga East Bull Lake Intrusive Suite in Ontario, Canada, is an example of a mafic igneous intrusion with 'contact-type' Ni-Cu- PGE sulfide mineralization along its base. Whereas many 'contact-type' deposits are thought to form from in situ contamination of the magma by the addition of crustal S during emplacement, there are some intrusions, including the RVI, which appear to have a much more complex history where the timing of S saturation, and thus the critical ore genesis processes, may have occurred much earlier, prior to emplacement. The RVI is made up of a basal ~100 m of unlayered, inclusion-bearing units, overlain by layered cumulates. The basal units contain autoliths of gabbroic rocks and inclusions of footwall gneiss and amphibolites, all within a gabbroic matrix. Platinumgroup element-rich magmatic sulfide mineralization occurs throughout both the inclusions and the matrix as blebby and disseminated sulfides. The matrix and inclusions can be separated into two distinct textural types: hydrothermally altered greenschist assemblages and unaltered metamorphic amphibolite assemblages. The platinum-group mineral (PGM) assemblages vary only between textural types, and not between inclusions and matrix, being dominated tellurides in all rock types. The hydrothermally altered rocks, however, have fewer tellurides, and an increased amount of Sb- and As-bearing PGM, indicative of minor fluid interaction, although the PGM have not been mobilised significantly away from the base metal sulfides. Precious and base metal geochemistry shows all rock types to have an excellent correlation between all the PGE, indicating the presence of a single, well homogenised, PGE-rich sulfide liquid. However, Au and Cu appear to be decoupled from the PGE at low concentrations, although correlate well with each other, which is interpreted to be due to minor fluid redistribution and alteration of sulfide bleb margins. The overlying Layered Units above the mineralized units are not PGE depleted. Trace element data, including (Th/Yb)PM and (Nb/Th)PM ratios, demonstrate that all River Valley rocks were formed from crustally contaminated magmas following interaction with local country rocks in a deeper subchamber; although some samples have S/Se ratiosindicative of crustal S, most have S/Se ratios lower than the mantle range, indicative of S loss. We propose a multi-stage model for the formation of the mineralization in the RVI with a major contamination event at depth with the addition of S from local crustal rocks, inducing sulfide saturation. Sulfide droplets were then enriched in PGE within a conduit system with possible further upgrading of sulfide metal tenors (and reduction of S/Se ratios) via partial dissolution of sulfide. The PGE-enriched sulfide liquid then settled in a staging chamber and partially crystallised before a major pulse of magma entrained sulfide liquid, eroded blocks of pre-crystallised and mineralized gabbro and footwall rocks and emplaced an inclusion-bearing package as the lower 100m or so of the RVI. Later emplacement of main RV magma was from a S-undersaturated, PGE-fertile magma. The RVI is thus an example whereby 'contact-type' mineralization is purely a function of the earliest magma intruded containing pre-formed sulfide mineralization, rather than contamination triggering sulfide saturation in situ. In such cases, processes at depth determine the generation and subsequent tenor of the mineralization. In particular, dissolution of the sulfide can upgrade metal tenor, but subsequently will reduce S/Se ratios, masking the signature of crustal contamination. In addition, a multi stage emplacement such as this will not necessarily preserve the characteristic increase in Cu/Pd ratios in the overlying cumulates that is often used in exploration for PGE deposits in mafic intrusions. Thus, a full understanding of all the field, geochemical and mineralogical factors is required to construct genetic models for such deposits, and especially in the interpretation of S/Se and Cu/Pd ratios as an indicator of crustal contamination and the presence of PGE mineralisation

Extreme enrichment of Se, Te, PGE and Au in Cu-sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

Extreme enrichment of Se, Te, PGE and Au in Cu-sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenlan

The use of magnetite as a geochemical indicator in the exploration for magmatic Ni-Cu-PGE sulfide deposits: a case study from Munali, Zambia

Magmatic sulfide deposits hosted by mafic-ultramafic intrusions are the most important source of Ni and PGE on Earth. Exploration strategies rely on geophysics to identify the host intrusions, and surface geochemistry to identify anomalous concentrations of Cu, Ni, Co, Cr, As and other associated elements. The use of geochemical indicator minerals in overburden is used widely in diamond exploration and mineral chemistry in fresh rock is increasingly used to identify proxies for mineralisation in magmatic-hydrothermal systems. However, no indicator mineral techniques are routinely applied to magmatic sulfides. Magnetite represents an ideal indicator mineral for this mineralisation style due to its ubiquity in such deposits, its resistance to weathering, its recoverability from soil samples, and its chemical variability under differing conditions of formation. We use the Munali Ni sulfide deposit to test the use of magnetite as an indicator mineral. Magnetite from mafic, ultramafic, and magmatic sulfide lithologies in fresh rock at Munali show discernible differences in the most compatible elements (V, Ni, Cr). We propose a new Cr/V versus Ni discrimination diagram for magnetite that can be used to indicate fractionation of the parent magma (Cr/V increases from ultramafic to mafic), and the presence of co-existing sulfides (Ni contents >300ppm). The signatures of these three elements at Munali are comparable to sulfide-related magnetites from other deposits, supporting the broad applicability of the discrimination diagram. Samples taken from overburden directly on top of the Munali deposit replicate signatures in the fresh bedrock, strongly advocating the use of magnetite as an exploration indicator mineral. Samples from areas without any geophysical or geochemical anomalies show weak mineralisation signatures, whereas magnetite samples taken from prospects with such anomalies display mineralisation signatures. Magnetite is a thus a viable geochemical indicator mineral for magmatic sulfide mineralisation in early stage exploration

Mineralogical and fluid characteristics of the fluorite-rich Monakoff and E1 Cu-Au deposits, Cloncurry region, Queensland, Australia : implications for regional F-Ba-rich IOCG mineralisation

The Monakoff iron oxide–Cu–Au (IOCG) deposit, located to the north east of Cloncurry within the Eastern Succession of the Mount Isa Inlier, Queensland, Australia, is characterised by high concentrations of F and Ba, with a host of other enriched elements including Co, Ag, Mn, REE, U, Pb, Zn and Sr. This gives the deposit a characteristic gangue assemblage dominated by fluorite, barite and calcite. The nearby E1 deposit, located 25 km to the NNE of Monakoff, and the large Ernest Henry deposit, 3 km to the west of E1, also contain abundant fluorite, barite and calcite in late stage assemblages. The three deposits, therefore, constitute a distinct group of IOCG deposits within the district, based on their F-rich geochemical and mineralogical affinities. The Monakoff ore zone is hosted in dilational openings along a shear zone developed within metasediments and metavolcanic rocks at the boundary between competent hangingwall rocks of the Toole Creek Volcanics and footwall rocks of the Mount Norna Quartzites. Four stages of alteration and mineralisation are recognised: Stage 1 garnet–biotite alteration; Stage 2 biotite–magnetite alteration; Stage 3 main F–Ba-ore mineralisation; and a Stage 4 pyrite–alloclasite Au–Co–As overprint. The E1 deposit has a more complex history, but Stage 5 has veins of fluorite–barite–carbonate that are comparable to Monakoff's main stage. The Stage 3 assemblage at Monakoff comprises a sheared groundmass of fluorite, barite, manganoan calcite, magnetite, chalcopyrite, pyrite, galena and sphalerite, with coarser grained pods of the same mineralogy interpreted to be dilational structures infilled during syn-ore deformation. Accessory minerals include U–Pb-oxides, REE–F-carbonates and Ag–Pb–Bi-sulfosalts, with no discrete Au minerals. The sulfosalts are interpreted to have formed from an immiscible Bi-melt within the mineralising fluid at temperatures higher than the melting point of Bi. The Stage 4 overprint at Monakoff contains pyrite and alloclasite. Laser ablation analyses of the sulphide minerals at Monakoff reveal that Stage 3 sulphides contain only trace amounts of Au (0.04 ppm in pyrite), although galena and chalcopyrite contain significant concentrations of Ag. Stage 4 pyrite and alloclasite, however, contain ~ 1 ppm Au in solid solution and mass balance calculations indicate the majority of bulk rock Au to be present in these minerals, although the majority of bulk Ag is present in Stage 3 sulphides. The Stage 5 veins at E1 have an identical gangue and accessory mineralogy to Stage 3 at Monakoff and differ in the sulphide mineralogy only in the lack of galena and sphalerite. Four fluid inclusion populations are identified within the fluorite at Monakoff: Group 1 is CO[subscript 2] rich; Group 2 is complex solid–liquid–vapour inclusions, with two groups based on homogenisation temperature (> 450 °C and 300–375 °C). Laser ablation-ICP-MS analyses indicate that these inclusions contain Cu, Pb, Zn, Fe, Mn, Mg, Ag, REE, U and Ba, but significantly no S, Se or Au; Group 3 are solid–liquid–vapour inclusions with a T[subscript h] of 200–275 °C, and contain Ba, Na, Mg, K and Br; and Group 4 are low salinity liquid–vapour inclusions. Group 1, 2 and 4 inclusions are also present in fluorite at E1. The REE geochemistry of fluorite from Monakoff and E1 is comparable and is characterised by a distinct positive Eu anomalies in all analyses, interpreted to indicate oxidising conditions at the time of high temperature ore deposition. The presence of abundant fluorite and barite is indicative of fluid mixing due to the insolubility of barite and fluorite and thus Ba and S, and Ca and F must have been introduced via different fluids. We propose that the oxidised fluid represented by the Group 2 inclusions and containing F, Ba, REE, U and base metals, mixed with a reduced, S-bearing fluid in a zone of dilation in the host shear zone that acted as a conduit for fluid flow during D[subscript 3] deformation. The source of the metal and F-rich fluid is likely to be the nearby granitic intrusions of the Williams–Naraku batholith, probably the Malakoff granite. This granite is also likely to be the source of the CO[subscript 2] represented by Group 1 fluid inclusions, and the REE, U, base metals and possibly Au, although the high Pb and Zn content of Monakoff and not E1 may suggest a local input of those elements at Monakoff. Stage 4 mineralisation overprints the F–Ba stage and is characterised by a Co–As–Au signature. At present it is unclear if this is a late stage, more reduced, evolution of the main ore fluid, or a separate mineralising event entirely. The presence of this F–Ba-metal-rich fluid has produced a distinctive style of IOCG mineralisation in the area to the north of Cloncurry. The probable link to the Malakoff granite implies that similar deposits may be present within several kilometres of the granite in suitable structural traps. Monakoff illustrates that although structurally controlled, the presence of Na–Ca alteration and ‘red rock’ K-alteration and brecciation are not key exploration criteria for these deposits. In addition, the presence of the overprinting As–Co–Au assemblage may indicate that this is a separate mineralising episode that may be present at other localities in the district. This study has also shown that fluorite can provide a powerful tool for determining ore forming conditions in F-rich IOCG systems

The Munali Ni sulfide deposit, southern Zambia: a multi-stage, mafic-ultramafic, magmatic sulfide-magnetite-apatite-carbonate megabreccia

The Munali Intrusive Complex (MIC) is a flattened tube-shaped, mafic-ultramafic intrusion located close to the southern Congo Craton margin in the Zambezi belt of southern Zambia. It is made up of a Central Gabbro Unit (CGU) core, surrounded by a Marginal Ultramafic-mafic Breccia Unit (MUBU), which contains magmatic Ni sulfide mineralisation. The MIC was emplaced into a sequence of metamorphosed Neoproterozoic rift sediments and is entirely hosted within a unit of marble. Munali has many of the characteristics of craton-margin, conduit-style, dyke-sill complex-hosted magmatic sulfide deposits. Three-dimensional modelling of the MUBU on the southern side of the MIC, where the Munali Nickel Mine is located, reveals a laterally discontinuous body located at the boundary between footwall CGU and hangingwall metasediments. Mapping of underground faces demonstrates the MUBU to have intruded after the CGU and be a highly complex, multi stage megabreccia made up of atypical ultramafic rocks (olivinites, olivine-magnetite rocks, and phoscorites), poikilitic gabbro and olivine basalt/dolerite dykes, brecciated on a millimetre to metre scale by magmatic sulfide. The breccia matrix is largely made up of a sulfide assemblage of pyrrhotite-pentlandite-chalcopyrite-pyrite with varying amounts of magnetite, apatite and carbonate. The sulfides become more massive towards the footwall contact. Late stage, high temperature sulfide-carbonate-magnetite veins cut the rest of the MUBU. The strong carbonate signature is likely due, in part, to contamination from the surrounding marbles, but may also be linked to a carbonatite melt related to the phoscorites. Ductile deformation and shear fabrics are displayed by talc-carbonate altered ultramafic clasts that may represent gas streaming textures by CO2-rich fluids. High precision U-Pb geochronology on zircons give ages of 862.39 ± 0.84 Ma for the poikilitic gabbro and 857.9 ± 1.9 Ma for the ultramafics, highlighting the multi-stage emplacement but placing both mafic and later ultramafic magma emplacement within the Neoproterozoic rifting of the Zambezi Ocean, most likely as sills or sheet-like bodies. Sulfide mineralisation is associated with brecciation of the ultramafics and so is constrained to a maximum age of 858 Ma. The Ni- and Fe-rich nature of the sulfides reflect either early stage sulfide saturation by contamination, or the presence of a fractionated sulfide body with Cu-rich sulfide elsewhere in the system. Munali is an example of a complex conduit-style Ni sulfide deposit affected by multiple stages and sources of magmatism during rifting at a craton margin, subsequent deformation; and where mafic and carbonatitic melts have interacted along deep seated crustal fault systems to produce a mineralogically unusual deposit

Sulphide sinking in magma conduits: evidence from mafic-ultramafic plugs on Rum and the wider North Atlantic Igneous Province

Ni–Cu–PGE (platinum group element) sulphide mineralization is commonly found in magmatic conduit systems. In many cases the trigger for formation of an immiscible sulphide liquid involves assimilation of S-bearing crustal rocks. Conceptually, the fluid dynamics of sulphide liquid droplets within such conduits is essentially a balance between gravitational sinking and upwards entrainment. Thus, crustal contamination signatures may be present in sulphides preserved both up- and down-flow from the point of interaction with the contaminant. We examine a suite of ultramafic volcanic plugs on the Isle of Rum, Scotland, to decipher controls on sulphide accumulation in near-surface magma conduits intruded into a variable sedimentary stratigraphy. The whole-rock compositions of the plugs broadly overlap with the compositions of ultramafic units within the Rum Layered Complex, although subtle differences between each plug highlight their individuality. Interstitial base metal sulphide minerals occur in all ultramafic plugs on Rum. Sulphide minerals have magmatic δ 34 S (ranging from –1·3 to +2·1‰) and S/Se ratios (mean = 2299), and demonstrate that the conduit magmas were already S-saturated. However, two plugs in NW Rum contain substantially coarser (sometimes net-textured) sulphides with unusually light δ 34 S (–14·7 to +0·3‰) and elevated S/Se ratios (mean = 4457), not represented by the immediate host-rocks. Based on the Hebrides Basin sedimentary stratigraphy, it is likely that the volcanic con duits would have intruded through a package of Jurassic mudrocks with characteristically light δ 34 S (–33·8 to –14·7‰). We propose that a secondary crustal S contamination event took place at a level above that currently exposed, and that these sulphides sank back to their present position. Modelling suggests that upon the cessation of active magma transport, sulphide liquids could have sunk back through the conduit over a distance of several hundreds of metres, over a period of a few days. This sulphide ‘withdrawal’ process may be observed in other vertical or steeply inclined magma conduits globally; for example, in the macrodykes of East Greenland. Sulphide liquid sinking within a non-active conduit or during magma ‘suck-back’ may help to explain crustal S-isotopic compositions in magma conduits that appear to lack appropriate lithologies to support this contamination, either locally or deeper in the system

Constraints on the development of orogenic style gold mineralisation at Mineral de Talca, Coastal Range, central Chile: evidence from a combined structural, mineralogical, S and Pb isotope and geochronology study

Mineral de Talca is a rare occurrence of Mesozoic, gold-bearing quartz vein mineralisation situated within the Coastal Range of northern Chile. Quartz veins are controlled by NNW-SSE trending faults are hosted by Devonian-Carboniferous metasediments of greenschist facies, and younger, undeformed granitoid and gabbro intrusions. The principle structural control in the area is the easterly dipping, NNW-SSE trending El Teniente Fault, which most likely developed as an extensional normal fault in the Triassic, but was later reactivated as a strike slip fault during subsequent compression. A dilational zone in the El Teniente Fault appears to have focussed fluid flow and an array of NW-SE-trending veins is present as splays off the El Teniente Fault. Mineralised quartz veins typically up to a metre thick occur in three main orientations: (1) parallel to and within NNW-SSE trending, E-dipping faults throughout the area; (2) along NW-SE trending, NE-dipping structures which may also host andesite dykes; (3) rarer E-W trending, subvertical veins. All mineralised quartz veins show evidence of multiple fluid events with anastomosing and cross cutting veins and veinlets, some of which contain up to 3.5 volume % base metal sulfides. Mineralogically, Au is present in three textural occurrences: (1) with arsenopyrite and pyrite in altered wall rock and along the margins of some of the veins; (2) with Cu-Pb-Zn sulfides within quartz veins; and (3) as nuggets and clusters of native Au within quartz. Fluid inclusion work indicates the presence of CO2-CH4-bearing fluids with homogenisation temperatures of ~350°C and aqueous fluids with low-moderate salinities (0.4-15.5 wt% NaCl eq) with homogenisation temperatures in the range 161- 321°C. The presence of Au with arsenopyrite and pyrite in structurally controlled quartz veins, in greenschist facies rocks with evidence of CO2-bearing fluids is consistent with an orogenic style classification for the mineralisation. However, the significant amounts of base metals, the moderate salinity of some of the fluids and the proximity to felsic granitoid intrusions have raised the possibility of an intrusion-related origin for the mineralisation. Vein sulphides display S isotope signatures (δ34S +2.1 to +4.3 ‰) that are intermediate between the host rock meta-sediments (δ34 S +5.3 to +7.5 ‰) and the local granitoids (δ34S +1.3 to +1.4 ‰), indicating a distinct crustal source of some of the S in the veins, and possibly a mixed magmatic-crustal S source. The local granite and granodiorite give U-Pb zircon ages of 219.6 ± 1 and 221.3 ± 2.8 Ma, respectively. Lead isotopic compositions of galena in the veins are consistent, suggesting derivation from a homogeonous source. Differences, however, between the isotopic signatures of the veins and igneous feldspars from nearby intrusions implies that these bodies were not the source of the metals though an igneous source from depth cannot be 3 discounted. The Triassic age of the granitoids is consistent with emplacement during regional crustal extension, with the El Teniente Fault formed as an easterly dipping normal fault. The change to a compressional regime in the mid Jurassic caused reactivation of the El Teniente Fault as a strike slip fault and provided a structural setting suitable for orogenic style mineralisation. The intrusions may, however, have provided a structural competency contrast that focused the mineralising fluids in a dilational jog along the El Teniente Fault to form WNW-trending veins. As such, the mineralisation is classed as orogenic style, and the identification of the key mineralogical, isotopic and structural features have implications for exploration and the development of similar deposits along the Coastal Range

A review of Te and Se systematics in hydrothermal pyrite from precious metal deposits: Insights into ore-forming processes

Pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including Au and Co and the semi-metals As, Se, Sb, Te and Bi. As such, in many hydrothermal ore deposits, where pyrite is the dominant sulphide phase, it can represent a major repository for these elements. Furthermore, the concentrations and ratios of Au, As and Co in pyrite have been used to infer key ore-forming processes. However, the mechanisms controlling the distribution of Te and Se in pyrite are less well understood. Here we compare the Te and Se contents of pyrite from a global dataset of Carlin-type, orogenic Au, and porphyry-epithermal deposits to investigate: (1) the potential of pyrite to be a major repository for these elements; and (2) whether Te and Se provide insights into key ore-forming processes. Pyrite from Carlin-type, low-sulphidation and alkaline igneous rock-hosted epithermal systems is enriched in Te (and Se) compared to pyrite from high-sulphidation epithermal and porphyry Cu deposits. Orogenic Au pyrite is characterised by intermediate Te and Se contents. There is an upper solubility limit for Te as a function of As in pyrite, similar to that established for Au by ; and this can be used to identify Te present as telluride inclusions, which are common in some epithermal-porphyry and orogenic Au deposits. Physicochemical fluid parameters, such as pH, redox and temperature, as well as crystal-chemistry control the incorporation and concentration of Se and Te in pyrite. Neutral to alkaline fluids have the ability to effectively mobilise and transport Te. Fluid boiling in porphyry-epithermal systems, as well as wall rock sulphidation and oxidation in Carlin-type (and orogenic Au) deposits can effectively precipitate Te in association with pyrite and Au. In contrast, Se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature, irrespective of pH and fO 2 . Hence, we propose that the Se contents of pyrite may be used asa new geo-thermometer for hydrothermal ore deposits. Furthermore, the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for Te and Se in Carlin-type and some epithermal systems, and thus pyrite can be considered to be of economic interest asa potential source for these elements