Chalcopyrite Inclusions Research Articles

Platinum-group elements in porphyry copper deposits: a reconnaissance study

Sulphide and flotation concentrates from 33 porphyry copper deposits have been investigated for platinum-group elements (PGE), Au, Cu and platinum-group minerals (PGM). The major sulphides in the samples studied are chalcopyrite and pyrite. Bornite is less frequent and molybdenite occurs in traces only. PGM (merenskyite, sperrylite and an unidentified Pd-Sb telluride) have been found as inclusions in chalcopyrite. Pd and Pt are present in concentrations above the analytical detection limit (> 8 ppb) in 70% respectively 30% of the deposits studied. The contents of Os, Ir, Ru and Rh are below detection limits in all samples. The analytical results show that 7 deposits (six of island arc and one of continental margin setting) reveal relatively high Pd contents (130–1900 ppb) which are associated with high Au contents (1–28 ppm). In five of them discrete PGM can be identified in accordance with elevated levels of Pd. Correlations of Au, Pd and Pt point towards a common origin. Even though the data base is relatively small, a trend is obvious, suggesting that Au-rich island arc porphyry copper deposits might host more Pd and Pt than the continental margin type ones. Other aspects of intrusive rocks, such as geological age, chemical composition and magma type do not seem to influence PGE contents.

Kinetics of iron depletion near pyrrhotite and chalcopyrite inclusions in sphalerite; the sphalerite speedometer

The textures and chemical compositions of sphalerite containing chalcopyrite and pyrrhotite inclusions from some skarns, together with experimental data on diffusivity, have permitted rates of exsolution (speedometry) and cooling histories of the skarns to be calculated. These calculations are based upon Fe depletion profiles obtained by electron microprobe transverses across those portions of sphalerite grains that are adjacent to chalcopyrite lamellae and pyrrhotite laths. The lamellae and laths occur within and along grain boundaries and polysynthetic twin planes in the host sphalerite. In addition, the samples contain 2- to 10-mu m chalcopyrite blebs that do not have the appearance of chalcopyrite disease textures.Two types of iron depletion profiles are observed in iron-rich sphalerite near sulfide inclusions: one type indicates a slight decrease in the Fe contents adjacent to chalcopyrite blebs, the other exhibits a larger Fe depletion (e.g., 3-6 mole % FeS over 70mu m) near chalcopyrite lamellae and pyrrhotite laths.Experimentally determined tracer diffusion rates of 59 Fe in sphalerite (D Fe = 5.6 x 10 (super -4) exp[-38 + or - 2 kcal/mole/RT], with a pyrrhotite + pyrite buffer) have been applied as a test to determine if Fe depletion can be explained by the simple cooling histories of the skarns. If all the sulfide inclusions are assumed to have been originally dissolved in Cu-bearing sphalerite at a higher temperature, the duration for isothermal precipitation of a chalcopyrite bleb from a sphalerite sphere of 50- mu m radius is calculated to be ca. 870 m.y. at 400 degrees C, the estimated temperature at which such a process may have taken place. Because of the slow Fe diffusivity in sphalerite, this time is unreasonably long, exceeding the geologic age (Mesozoic) of the deposits under consideration, so exsolution of chalcopyrite blebs from homogeneous sphalerite is unlikely. In contrast, the profiles of sharp Fe depletion in sphalerite are presumed to have developed during reequilibration of Fe-rich sphalerite attending the exsolution of pyrrhotite laths in response to decreasing temperature and rising sulfur fugacity. The measured profiles near pyrrhotite laths have been simulated by finite difference approximations to Fick9s diffusion equation. For an exsolution process starting at 350 degrees C and with a cooling rate of 0.5 degrees C/1,000 yr, the observed Fe depletion profiles would have been frozen in within 210,000 yr and with a closure temperature estimated to be 245 degrees C.

Precious metal mineralogy in porphyry-, skarn-, and replacement-type ore deposits of the Ertsberg (Gunung Bijih) District, Irian Jaya, Indonesia

Petrographic and electron microprobe analyses of native Au and a variety of sulfide minerals indicate a generally high but widely varying native Au fineness and a Cu-Fe sulfide host for most Ag in the Gunung Bijih Timur complex of Cu-Au skarn deposits, the Big Gossan and Dom Cu skarn deposits, and the Grasberg porphyry Cu-Au deposit. Native Au rims bornite in veins and forms inclusions in bornite and chalcopyrite in samples from Grasberg and from the Gunung Bijih Timur complex, as well as filling open space in quartz veins in the complex. Skarn and quartz veins in the Big Gossan area host native Au in association with pyrite, pyrrhotite, galena, chalcopyrite, sphalerite, and arsenopyrite.Native Au from the Gunung Bijih Timur complex has a wide but bimodal range of fineness: 920 to 990 and 340 to 820 (avg = 860). Native Au from Grasberg samples is < or = 930 fine (avg = 960). Fineness of Big Gossan Au ranges from 540 to 960 (avg = 830), although compositional ranges are small within most individual samples. Native Au from Grasberg falls into two groups with respect to Pd: Pd-bearing (< or = 3,500 ppm; avg = 1,800 ppm) and with no detectable Pd. Fire assay of Grasberg ore reveals trace but detectable (10 ppb < [Pd] < 500 ppb, avg = < or = 50 ppb) concentrations of Pd and no detectable Pt. Native Au from the Gunung Bijih Timur complex averages twice as much Cu as that from Grasberg (1.7 vs. 0.8 wt % Cu). Native Au from Big Gossan has uniformly low Cu contents (< or = 1,200 ppm Cu; avg = 300 ppm).Mass-balance calculations and analytical data indicate that the bulk of the Ag in the Gunung Bijih Timur complex is contained by bornite, indicating a partitioning of Ag into bornite, relative to native Au or a discrete Ag mineral. This is supported by the consistent positive correlation of Cu and Ag throughout the Gunung Bijih Timur complex, as well as in Grasberg and Dom. Ag-bearing galena occurs in the Big Gossan area, but is rare in the Grasberg, the Gunung Bijih Timur complex, and the Dom orebodies.The high fineness of native Au from the Gunung Bijih district represents the upper end of the reported range for porphyry- and skarn-type Cu-Au deposits but is similar to values reported elsewhere in Indonesia. The fineness of native Au in the Gunung Bijih Timur complex does not appear to be controlled by depth or distance from the local intrusive contact, mineral assemblage, or paragenetic relationship. The fineness of native Au from the Big Gossan area shows a positive correlation with elevation, suggestive of a lower temperature, more distal character than in the other skarns of the district. Differences in Pd contents may be related to acidity and redox conditions during native Au deposition.High Cu, high Pd, and low Ag compositions of Au grains in pan concentrates suggest a porphyry or Cu skarn source relative to a more distal source. Compositional characteristics identified in this study may have applications to exploration within the Ertsberg district and elsewhere.

An SEM examination of the chalcopyrite disease texture and its genetic implications

AbstractBack-scattered electron imaging with a scanning electron microscope was applied to the intimate association of fine chalcopyrite grains and sphalerite (‘chalcopyrite disease’) in synthesized products and natural specimens, in order to distinguish between diagnostic features of two formation mechanisms: replacement and coprecipitation. In the synthetic chalcopyrite disease in Fe-bearing sphalerite formed by a replacement reaction, chalcopyrite occurs as fine lamellae, which are also observed in relatively Fe-rich growth bands of the natural zoned sphalerite. Ellipsoidal to lens-like habits of chalcopyrite appear in sphalerite that has undergone extensive replacement reactions. These textures may have grown steadily from the lamellar chalcopyrite by consuming the FeS component dissolved in the sphalerite. All the sphalerite samples formed by the coprecipitation mechanism are Fe-poor, hosting triangular or irregularly bleb-like inclusions of chalcopyrite. This variety of chalcopyrite morphology could be attributed to diffusion rates and variations in fluid saturation, and their effect on the rate of crystal growth. Thus, in both replacement and coprecipitation the chalcopyrite habit depends strongly both on the FeS content of the host sphalerite and on kinetic factors, and is significant when interpreting chalcopyrite disease textures in natural samples.

Florencite-(La) with fissiogenic REEs from a natural fission reactor at Bangombe, Gabon

Florecite-(La) (La/Ce = 1.09) with fissiogenic REEs and florecite-(Ce) (La/Ce = 0.62) have been identified in illite from the clay mantle surrounding a natural, 2 Ga fission reactor at Bangombre and in sandstone beneath the reactor zone, respectively. Florencite-(Ce) is apparently unrelated to nuclear processes and occurs with monazite-(Ce), apatite, TiO{sub 2} (probably anatase), zircon, and illite. Grains of florencite-(Ce) contain inclusions of thorite, chalcopyrite, and galena. Florencite-(La) was found 5 cm from the {open_quotes}core{close_quotes} of the reactor and contains inclusions of galena and U-Ti-bearing phases. Secondary uraninite and coffinite have precipitated on some of the florencite grains. The chemical composition of florencite-(La) as determined by electron microprobe analysis is (La{sub 0.38}Ce{sub 0.35}Nd{sub 0.06}Sm{sub 0.01}-Ca{sub 0.03}Sr{sub 0.17})(Al{sub 2.98}Fe{sub 0.02}{sup 3+})(PO{sub 4})[PO{sub 3.80}(OH){sub 0.20}](OH){sub 6}. Secondary ion mass spectrometry revealed that between 27 and 30% of Nd and 67 and 71% of Sm in florencite-(La) is fissiogenic. The presence of fissiogenic REEs in {open_quotes}florencite{close_quotes} from the reactor zone in Bangombe and their preferential concentration in florencite relative to the bulk sample of clay demonstrate that aluminous phosphates may have played a more significant role in the fixation of fissiogenic REES released from uraninite after the sustained fission reactions than sorption ontomore » clays. 30 refs., 3 figs., 2 tabs.« less

Trace elements in sulfide minerals from eastern Australian volcanic-hosted massive sulfide deposits; Part I, Proton microprobe analyses of pyrite, chalcopyrite, and sphalerite, and Part II, Selenium levels in pyrite; comparison with delta 34 S values and implications for the source of sulfur in volcanogenic hydrothermal systems

Part I. Pyrite, chalcopyrite, and sphalerite from six volcanic-hosted massive sulfide (Mount Chalmers, Rosebery, Waterloo, Agincourt, Dry River South, and Balcooma) deposits in eastern Australia were analyzed using a proton microprobe to determine trace element abundances. In pyrite, trace elements can be divided into three groups according to the most likely occurrence of the element: (1) elements that occur mainly as inclusions (Cu, Zn, Pb, Ba, Bi, Ag, and Sb), (2) elements that occur as nonstoichiometric substitutions in the lattice (As, Tl, Au, and possibly Mo), and (3) elements that occur as stoichiometric substitutions for Fe (Co and Ni) or S (Se and Te). Hydrothermal and metamorphic recrystallization cleans pyrite of group 1 and group 2 elements, but does not appear to affect the concentrations of group 3 elements. Colloform pyrite grains have the highest levels of As and Au (up to 200 ppm), suggesting that rapid precipitation is important in incorporating Au into auriferous pyrite. Elements that occur as inclusions in chalcopyrite include Pb, Bi, Zn (P), and Ba. The occurrence of As and Sb is unresolved, although consistently high values of As in some samples suggest that As may substitute into the lattice of chalcopyrite. Elements that substitute into the lattice include Ag (for Cu), In, Sn and Zn (?) (for Fe), and Se (for S). Lead, Ba, Sb, possibly, and in some cases, Cu, occur commonly as inclusions in sphalerite. Lattice substitutions in sphalerite include Fe, Cd, Cu (to 4,500 ppm), Ni, In, Ag, Te, Ga and possibly Mo. In addition, consistently high (2,000-4,000 ppm) levels of As in the Rosebery barite zone may indicate As lattice substitution. Part II. The Se content of pyrite in volcanic-hosted massive sulfide deposits varies as follows: in Cu-poor, Zn-rich deposits, Se levels are low (mainly <5 ppm) throughout; in Cu-rich deposits, Se levels are highest (10-200 ppm) in stringer zones and the lower part of the massive sulfide lens, and decrease toward the top of the massive sulfide lens and into peripheral altered rocks. Metamorphic recrystallization does not affect these variations. Although delta 34 S values also vary systematically in individual deposits, no systematic differences were noted between Cu-rich and Zn-rich deposits...

Platinum-group minerals in the Santo Tomas II (Philex) porphyry copper-gold deposit, Luzon Island, Philippines

Mineralized quartz diorites of the Santo Tomas II porphyry copper-gold deposit, carry high Au contents (average: 1.8 ppm) as well as 160 ppb Pd and 38 ppb Pt. Values of other platinum-group elements (PGE) and rhenium are below the analytical detection limits. There is a significant positive correlation between Au and Cu. The highest Pd values were detected in the most Au- and Cu-rich rocks. Platinum-group minerals (PGM) occur exclusively as inclusions in chalcopyrite and bornite. Potential Pd and Pt contents in sulphide concentrates are estimated at 1.5 g/t and 0.4 g/t, respectively. The precious metal assemblages consist of merenskyite (main PGM), kotulskite, moncheite, native gold, electrum, hessite and petzite. Polyphase fluid inclusions in quartz veinlets, associated with a PGM-bearing bornite-chalcopyrite-magnetite assemblage, are characterized by high salinity (35 to > 60 eq. wt% NaCl) and high trapping temperatures (between 380 and 520 °C). They may represent primary magmatic-hydrothermal fluids, which have been responsible for the transport of Pd, Pt and Au as chloride complexes.

Bismuth sulphosalts within quartz veining hosted by the Loch Shin monzogranite, Scotland

AbstractThe Loch Shin monzogranite is host to quartz veins bearing the sulphosalts aikinite, hammarite, lindströmite, krupkaite, gladite and pekoite, which belong to the aikinite-bismuthinite series, and represents the first significant occurrence of this series in the United Kingdom. Inclusions of the sulphotelluride tetradymite occur in krupkaite-gladite. Berryite is present as inclusions in chalcopyrite. Electron microprobe analyses reveal a range of compositions in individual crystal masses from hammarite to krupkaite in one sample, and from krupkaite to gladite in a second. Compositions between friedrichite and hammarite and gladite and pekoite are notably absent.

Gold skarn mineralization and fluid evolution in the Nickel Plate Deposit, British Columbia

The Nickel Plate orebody in the Hedley district is the largest gold skarn deposit in Canada. During the period 1904 to 1955 it produced almost 49 million metric tons (Mt) of gold representing approximately half of the gold produced from all skarns in British Columbia. The deposit is hosted by thinly bedded calcareous and tuffaceous siltstones and limestones of the Upper Triassic Nicola Group, an accreted oceanic-arc assemblage. These rocks are intruded by numerous sills, dikes, and small stocks of subalkalic, calc-alkaline quartz diorite, diorite, and gabbro. Skarn alteration and related gold mineralization overprints sedimentary and igneous rock and is zoned about the intrusive contacts.The early stages of alteration are marked by the formation of biotite, potassium feldspar, and quartz hornfels in siltstone and by potassic alteration of intrusive rock. The biotite contains <0.55 mole fraction phlogopite (Mg/(Mg + Fe)) and <2 wt percent TiO 2 which are features indicative of the reduced nature of this mineralization compared to that of porphyry Cu systems. This early stage of alteration is temporally continuous into formation of pyroxene skarnoid which consists of intermediate pyroxene (Hd (sub 48-59) ) in siltstone and Mg-rich pyroxene (Hd (sub 5-30) ) and K feldspar in intrusive rocks. The most volumetrically important alteration style, and the primary host to gold mineralization, consists of dark green, fine-grained pyroxene (Hd (sub 60-94) ) and lesser grandite garnet (Ad (sub 14-82) , avg Ad 35 ) which overprints earlier hornfels and skarnoid, and often completely replaces both sedimentary and igneous protoliths. Ore-bearing sulfides and scapolite occur with the hedenbergite skarn and consist of pyrrhotite, arsenopyrite with inclusions of gold, hedleyite, native bismuth, and minor chalcopyrite, sphalerite, and galena. Retrograde alteration in the deposit is limited, with only minor to trace amounts of wollastonite, prehnite, epidote, and chlorite replacing garnet and pyroxene.Fluid inclusion homogenization temperatures indicate that the main body of pyroxene-garnet skarn formed at an average temperature (pressure corrected) between 460 degrees and 480 degrees C with locally high temperatures of 700 degrees to 800 degrees C. Fluid salinities average 18.3 and 9.7 wt percent NaCl equiv for garnet and pyroxene, respectively. Dissolution temperatures of halite daughters in pyroxene and quartz from skarn indicate a maximum fluid salinity of 37.9 wt percent NaCl equiv. Homogenization temperatures in scapolite associated with sulfide mineralization indicate a lower temperature for this mineralization in the range 320 degrees to 400 degrees C.Estimated physiochemical conditions of formation based on the composition and stability fields of major calc-silicate and sulfide minerals indicate that the hedenbergite skarn, pyrrhotite, and arsenopyrite were deposited under similar conditions of sulfur fugacity (log f (sub S 2 ) = -10 to -3) and temperature (400 degrees -600 degrees C), whereas a log f (sub O 2 ) = -25 to -22 is estimated for the hedenbergite skarn.Spatial trends in pyroxene and garnet composition and the distribution of fluid inclusion homogenization temperatures indicate that the eastern contact of the Toronto stock and the locus of diorite dikes, such as the South dike, in the ore zone acted as critical conduits for channeling of hydrothermal fluids. These two separate fluid paths may have resulted in the two different compositional trends found in the pyroxene and garnet from locations in the ore zone versus those more proximal to the Toronto stock.

The nature of chalcopyrite inclusions in sphalerite; exsolution, coprecipitation, or "disease"?; reply

The nature of chalcopyrite inclusions in sphalerite; exsolution, coprecipitation, or "disease"?; reply

The nature of chalcopyrite inclusions in sphalerite; exsolution, coprecipitation, or "disease"?; discussion

The nature of chalcopyrite inclusions in sphalerite; exsolution, coprecipitation, or "disease"?; discussion

The nature of chalcopyrite inclusions in sphalerite; exsolution, coprecipitation, or "disease"?

Chalcopyrite inclusions in sphalerite, once considered to be only exsolution poducts, have been suggested to be replacements of Fe-rich sphalerite. This study reveals that (1) chalcopyrite inclusions were found in sphalerite with different iron contents: both Fe-poor varieties from 0.5 to 2 wt percent and Fe-rich, from 8 to 14 wt percent; (2) chalcopyrite inclusions were produced by replacement as the result of interaction of sphalerite with solutions, which transported both copper and iron; and (3) coprecipitation of sphalerite and chalcopyrite is an alternative mechanism of formation of the chalcopyrite inclusions in the ore deposits studied.

Platinum-group element and gold contents in the Skouries porphyry copper deposit, Chalkidiki Peninsula, northern Greece

The Skouries porphyry copper deposit is located in the eastern Chalkidiki peninsula, northern Greece. Along with several other porphyry copper occurrences, this deposit establishes the northeastern part of the Servomacedonian zone as a porphyry copper region. Amphibolite, mica schist, and two-mica gneiss are the predominant rock types exposed in the Skouries area. These rocks have been intruded by the Skouries porphyry stock, which is of subalkaline composition and is Tertiary in age (18 Ma). The Skouries porphyry intrusion and the surrounding country rocks are strongly fractured and intensely altered by hydrothermal fluids. In addition to intense silicification, a prominent alteration type is potassic, whereas phyllic and propylitic types are less common.Mineralization mainly includes chalcopyrite, pyrite, bornite, chalcocite, and magnetite in the form of veins, stockworks, and disseminations. Native gold and electrum commonly are present as small inclusions in chalcopyrite. Although lateral zoning is not defined clearly, a vertical zoning in terms of both metal mineralogy and overall metal content is apparent. A zone of oxidation (azurite-malachite) covers the upper part of the ore and is underlain by a zone of reduced rock rich in covellite and chalcocite, which in turn is underlain by the most important ore type, including a chalcopyrite-pyrite-bornite-magnetite assemblage.Both weakly and intensively altered porphyry samples from the deposit were analyzed for major oxides, trace elements, and all platinum-group elements (PGE). The stock exhibits high levels of Cu, Au, Ag, B, Bi, Co, Se, and Te. Barium and Sr contents are also high while Rb is low, resulting thereby in high K/Rb and low Rb/Sr ratios. Palladium concentrations range from less than 2 to 480 ppb. Ruthenium content ranges from 8 to 41 ppb and Pt from 2 to 10 ppb. Osmium, Ir, and Rh content is below detection limit. The average Au/Ag ratio is 0.87, which is consistent with the range of several worldwide porphyry copper deposits.On the basis of factor analysis of selected geochemical data, a strong positive interelement correlation (r > or = 0.83) between Au, Ag, Pd, nd Te coupled with their association with silica appears to support a correlation of these precious metals with silicification rather than potassic-type alteration. Such a relationship may suggest similar behavior of these metals and a common origin. A positive correlation of Cu with iron (r = 0.86), which is consistent with the association of chalcopyrite with magnetite, and the low correlation of Te and Pd with Cu may suggest that these metals and, to a lesser extent, copper have been redistributed during a late stage of evolution of the Skouries porphyry system. Furthermore, the close association of Te with precious metals, combined with the relatively low temperature for telluride minerals stability, may indicate that at least partly precious metal tellurides have been formed in a relatively shallow and less hot environment.

Tellurides, selenides and associated minerals in the Tunaberg copper deposits, SE Bergslagen, Central Sweden

The Tunaberg copper deposits, SE Bergslagen, Central Sweden, locally contain tellurium and selenium minerals not previously reported from this locality. Hessite, tellurobismutite, tellurium, tetradymite, kawazulite, clausthalite and selenian galena are found as inclusions in bornite and chalcopyrite in a skarn sulphide ore with Cd-rich sphalerite, cobaltite and cobalt pentlandite (assemblage A), and in a skarn iron ore with magnetite (assemblage B). Accessory minerals included in bornite and chalcopyrite are auriferous silver, electrum, carrollite, stannoidite, mawsonite, parkerite, aikinite, emplectite, wittichenite and two unidentified Cu-Ag-Bi sulphosalts. The tellurides, selenides and associated minerals in assemblage A occur, in part, as early crystallites and, in part, as segregations from a high-temperature bornite solid solution, which presumably crystallized from metamorphogenic skarn-forming ore solutions, about contemporaneous with the formation of diopside above 475°C and of retrogressive tremolite above 420°C. Minerals of Bi-Te-Se-Pb-Ag in assemblage B presumably crystallized at lower aS2 and higher aCu+ from residual hydrothermal solutions of similar metamorphogenic origin.

Indium-bearing chalcopyrite and sphalerite from the Gåsborn area, West Bergslagen, central Sweden

AbstractIn the Gåsborn area, West Bergslagen, central Sweden, Fe-rich, indium-bearing (0.1–2.0wt.% In) sphalerite is replaced by Fe-poor sphalerite containing minute inclusions of chalcopyrite, roquesite and an unnamed In-Zn-rich phase. Fe-rich, In-bearing sphalerite is primary; indium occurs as a roquesite molecule in solid solution. Fe-poor sphalerite, roquesite, chalcopyrite and the unnamed In-Zn-rich phase were formed from In-bearing sphalerite by secondary processes, characterized by the so-called ‘chalcopyrite disease’.

Sphalerite stars in chalcopyrite: Are they always the result of an unmixing process?

Sphalerite skeletal crystals in inclusions in chalcopyrite (so-called sphalerite stars) are widely thought to be the result of high-temperature unmixing processes. Detailed observations in the chalcopyrite ores at Ain Barbar (Algeria) demonstrate that the unmixing theory cannot work in this case. It is here proposed that skeletal crystals are the result of a local supersaturation in sphalerite at the growing fronts of chalcopyrite. This implies a high precipitation rate, estimated to be ca. 10-6 m sec-1, remaining compatible, however, with a recharge in ore-forming components by the flowing mineralizing solutions. In addition to Ain Barbar, this explanation is probably of more general significance since the kind of relationships described here is by no means restricted to this particular deposit.

Indium and germanium in the structure of sphalerite: an example of coupled substitution with Copper

The distribution of indium in sphalerite from hydrothermal veins in the Saint-Martinla-Sauvete district (Loire, France) was studied by microprobe. Several hundred analyses were carried out. Sphalerite, devoid of chalcopyrite inclusions, exhibits an oscillatory zoning which can be related to the variation of minor-element concentrations. Indium (up to 1.05 wt. %) is positively correlated with copper, and Cd with Fe. The distribution of these two pairs of elements is antithetic within (110) growth zones. In and Cu show a very complex distribution within some twinned sphalerite crystals and are preferentially concentrated in {111} growth zones. A variation of diffusion/growth velocity ratio is evoked to explain this behaviour. From core to rim of sphalerite crystals the Cd concentration decreases and that of In (and Cu) increases. This increase corresponds to the development of {111} faces, which become progressively more prominent. The slope of the regression line calculated from Cu and In values corresponding to In < 0.4 wt. % is subparallel to (Cu/In)at = 1. This indicates the substitution mechanism Cu(I) + In(III) ⇄ 2 Zn(II). However, the Cu concentration is generally higher than required by this equation. Cuex rises toward the rim of sphalerite crystals; Cu-rich and In-free zones exist in some crystals. Cuex concentration is generally above the CuS solubility limit in sphalerite. It is suggested that Fe(III) could assume the local charge balance of Cu(I). This hypothesis is compatible with the rise of Cuex in late growth zones and with the late crystallization of chalcopyrite with respect to sphalerite observed in these deposits. Consequently, the incorporation of In and Cu in sphalerite from the Saint-Martin-la-Sauvete district is governed by the following equation: M(I) + M(III) ⇄ 2 Zn(II), where M(I) = Cu; M(III) = In, Fe.

Sphalerite geobarometry in metamorphic terranes: an appraisal with implications for metamorphic pressure in the Otago Schist

Abstract Sphalerite geobarometry has long been known to give poor results when applied to regional metamorphic terranes. Application of the sphalerite geobarometer to three low‐to medium‐grade sulphide deposits—the Moke Creek and Waitahuna deposits, Otago, and the Goose Cove deposit, Newfoundland—yields pressures up to 9 kbar, which appear to be too high when compared with other geological data. Textural and mineralogical relationships suggest that the Goose Cove and, possibly, the Moke Creek deposits lacked the required equilibrium assemblage (pyrite + hexagonal pyrrhotite + sphalerite) during peak metamorphic conditions, rendering the geobarometer inapplicable. In addition, all three deposits show evidence of re‐equilibration at T &lt; 300°C, which has resulted in decreased FeS contents and high apparent pressures. Analyses of sphalerites from very low‐grade metachert from South Georgia Island, which contains the assemblage sphalerite + pyrite + monoclinic pyrrhotite + chalcopyrite, confirm that low‐temperature equilibration of this assemblage results in approximately 10–11 mol. % FeS in sphalerite. Comparison of these results with published descriptions of other deposits suggests that lack of the appropriate assemblage and retrograde re‐equilibration of sphalerite probably account for most anomalously high‐pressure estimates. Erratic compositions of sphalerites containing chalcopyrite inclusions may result from replacement of high‐temperature intermediate solid‐solution by chalcopyrite during cooling. Strain may enhance retrograde re‐equilibration of sphalerite by grain‐size reduction or dislocation‐assisted diffusion and/or nucleation. Re‐evaluation of the data from Moke Creek suggests that the sulphides experienced pervasive greenschist facies re‐equilibration at pressures of about 4.5 kbar, with late stage mobilization at about 2.8 kbar, and thus sphalerite compositions are not likely to reflect blueschist facies conditions. Pressure estimates based on sphalerite geobarometry should take into account at what stage in the history of a metamorphic terrane the sphalerite composition equilibrated.

Hydrogen and Oxygen Isotopic Compositions of Fluid Inclusions in the Kuroko Deposits, Japan

Initial data on the hydrogen and oxygen isotopic compositions of water in fluid inclusions in pyrite and chalcopyrite from some of the Kuroko deposits in the Hokuroku district of Japan fall within a narrow range: delta D = -- 26 to --18 per mil and delta 18 O = --1.6 to -0.3 per mil, relative to SMOW.These data together with geologic and other geochemical data indicate that the Kuroko ore fluids were predominantly of sea-water origin. A small proportion (less than 25 percent) of magmatic and/or meteoric water may have been mixed in the ore fluids.A model for the formation of the ores by convective circulation of sea water through high-temperature volcanic rocks is presented.

Paragenetic relations of some Cu-Fe-Sn-Sulfides in the Mangualde pegmatitie, North Portugal

The textures of chalcopyrite from the Mangualde pegmatite suggest: a) myrmekitic intergrowths of chalcopyrite and complex stannite-kesterite-hexastannite inclusions formed by reactions involving: 1, eutectoid unmixing of Sn-Zn-bearing chalcopyrite solid solution into chalcopyrite and Zn-bearing stannite, 2, formation of hexastannite by reaction of the stannite with chalcopyrite, whereby kesterite formed as an intermediate product; b) chalcopyrite-hexastannite myrmekites crystallized as cotectic precipitates from liquid; hexastannite was partly replaced and rimmed by mawsonite during subsequent cotectic crystallization of chalcopyrite-mawsonite myrmekites; c) stannite inclusions in cubanite-bearing chalcopyrite formed by exsolution; d) in bornite-rich samples bornite and hexastannite crystallized before chalcopyrite. Phase relations in the pseudo-ternary cubanite-stannite-bornite Zn-bearing system are depicted; the association bornite-stannite is incompatible at lower temperatures, as below about 500 °C hexastannite and mawsonite intervene as intermediate compounds.