Fluid Inclusions, Stable Isotopes and Geochemistry of Porphyry Copper and Epithermal Vein Deposits of the Hauraki Gold - Silver Province, New Zealand

<p>Tertiary epithermal Au-Ag-Pb-Zn-Cu vein, and porphyry copper deposits occur in the Hauraki Province. The epithermal deposits were extensively mined for gold and silver in the late 1800's, and early 1900's and produced approximately 300 million grams (10 million ounces) of gold and 1,000 million grams (30 million ounces) of silver. They occur in Jurassic greywacke suite rocks, lower Miocene-Pliocene andesites and dacites, and upper Miocene-Pleistocene rhyolites although the deposits in the and esites and dacites produced most of the gold and silver mined. Base metal assemblages of the epithermal deposits are dominated by pyrite, sphalerite, galena and chalcopyrite, whereas acanthite and native gold (electrum) are the most common precious metal minerals. Tellurides (e.g. hessite) and seleniferous - selenide minerals are locally important. Gangue minerals are mainly quartz and calcite. Near neutral or slightly alkaline fluid pH is indicated for the epithermal fluids by the occurrence of sericite and/or adularia in wall rock alteration mineral assemblages. Acidic fluids, forming kaolinite, are characteristic of late stages or near surface environments. Fluid inclusion filling temperatures, and sulphur isotope temperatures from sphalerite-galena pairs, indicate that base metal deposition occurred mainly between 320 and. 280 degrees C, precious metal assemblages predominantly in the range of 280 - 200 degrees C and late stage barite, in some deposits, generally below 200 degrees C. There is fluid inclusion evidence for boiling during mineralisation in some deposits. Apparent salinities of the epithermal fluids, determined from fluid inclusion freezing temperatures, range from 0 - 6.1 eq. wt. % NaCl. No consistent difference in average apparent salinity was recognised between the different types of epithermal deposits, although the highest recorded values were from the base metal deposits. The absence of liquid CO2 in fluid inclusions limits the maximum possible concentration of CO2 to approximately 3 mole %. Extraction and measurement of CO2, from some samples indicates an average concentration of approximately 1 mole %. Corrections for dissolved CO2 required to transform apparent salinities to true salinities indicate that CO2 is the major solute in low salinity inclusions and that its concentration varied widely during mineral deposition in most deposits. Thermodynamic models of the geochemical environments of mineral deposition indicate that the large gold-silver deposits were formed by solutions in which sulphur occurred predominantly in reduced form, whereas many other deposits formed from solutions with approximately equal concentrations of oxidised and reduced aqueous sulphur species. Mineral deposition resulted from several different processes including: changes in fluid pH accompanying reactions with the wall rocks, mixing with other types of fluids, boiling, and variations in the concentration of CO2 in solution. These various processes acted separately in different parts of the hydrothermal system and general deposited characteristic mineral assemblages. Deuterium/hydrogen ratios of water extracted from fluid inclusions indicate that most hydrothermal fluids were originally meteoric water. Sulphur isotope ratios of sulphide and sulphate minerals, in association with the thermodynamic relations of the mineral assemblages, indicate that the sulphur was derived from at least two different sources; sedimentary sulphate and magmatic SO2, the relative importance of each varying from one deposit to another. Two types of hydrothermal systems are postulated for the formation of the epithermal deposits. During andesitic volcanism in the Miocene-early Pliocene, hydrothermal fluid convective cells were generated by heat from near surface small intrusive bodies of magma, whereas during rhyolitic volcanism in the late Miocene-Pleistocene the heat sources were larger plutons at greater depth. Porphyry copper deposits are associated with quartz diorite stocks intruded into Jurassic greywacke suite rocks and Miocene andesites. They are "diorite" model hypabyssal and volcanic types. The major minerals are quartz, pyrite, chalcopyrite and sphalerite. Additional minerals differ between the different deposits and define two contrasting geochemical environments of deposition, one characterised by low fS2, fO2 and Sigma S, indicated by the presence of pyrrhotite, and the other of moderate to high fS2, fO2 and Sigma S, indicated by the occurrence of bornite, magnetite or hematite. Associated hydrothermal alteration is generally propylitic although limited phyllic and "potassic" (defined by secondary biotite) types also occur in some deposits. Fluid inclusion and sulphur isotope studies of the Miners Head. porphyry copper deposit suggest that copper mineralisation occurred at a temperature of approximately 425 degrees C from fluids with apparent salinities up to.15.5 eq. wt. % NaCl and containing sulphur of magmatic origin, predominantly as H2S.</p>

Fluid Inclusions, Stable Isotopes and Geochemistry of Porphyry Copper and Epithermal Vein Deposits of the Hauraki Gold - Silver Province, New Zealand

<p>Tertiary epithermal Au-Ag-Pb-Zn-Cu vein, and porphyry copper deposits occur in the Hauraki Province. The epithermal deposits were extensively mined for gold and silver in the late 1800's, and early 1900's and produced approximately 300 million grams (10 million ounces) of gold and 1,000 million grams (30 million ounces) of silver. They occur in Jurassic greywacke suite rocks, lower Miocene-Pliocene andesites and dacites, and upper Miocene-Pleistocene rhyolites although the deposits in the and esites and dacites produced most of the gold and silver mined. Base metal assemblages of the epithermal deposits are dominated by pyrite, sphalerite, galena and chalcopyrite, whereas acanthite and native gold (electrum) are the most common precious metal minerals. Tellurides (e.g. hessite) and seleniferous - selenide minerals are locally important. Gangue minerals are mainly quartz and calcite. Near neutral or slightly alkaline fluid pH is indicated for the epithermal fluids by the occurrence of sericite and/or adularia in wall rock alteration mineral assemblages. Acidic fluids, forming kaolinite, are characteristic of late stages or near surface environments. Fluid inclusion filling temperatures, and sulphur isotope temperatures from sphalerite-galena pairs, indicate that base metal deposition occurred mainly between 320 and. 280 degrees C, precious metal assemblages predominantly in the range of 280 - 200 degrees C and late stage barite, in some deposits, generally below 200 degrees C. There is fluid inclusion evidence for boiling during mineralisation in some deposits. Apparent salinities of the epithermal fluids, determined from fluid inclusion freezing temperatures, range from 0 - 6.1 eq. wt. % NaCl. No consistent difference in average apparent salinity was recognised between the different types of epithermal deposits, although the highest recorded values were from the base metal deposits. The absence of liquid CO2 in fluid inclusions limits the maximum possible concentration of CO2 to approximately 3 mole %. Extraction and measurement of CO2, from some samples indicates an average concentration of approximately 1 mole %. Corrections for dissolved CO2 required to transform apparent salinities to true salinities indicate that CO2 is the major solute in low salinity inclusions and that its concentration varied widely during mineral deposition in most deposits. Thermodynamic models of the geochemical environments of mineral deposition indicate that the large gold-silver deposits were formed by solutions in which sulphur occurred predominantly in reduced form, whereas many other deposits formed from solutions with approximately equal concentrations of oxidised and reduced aqueous sulphur species. Mineral deposition resulted from several different processes including: changes in fluid pH accompanying reactions with the wall rocks, mixing with other types of fluids, boiling, and variations in the concentration of CO2 in solution. These various processes acted separately in different parts of the hydrothermal system and general deposited characteristic mineral assemblages. Deuterium/hydrogen ratios of water extracted from fluid inclusions indicate that most hydrothermal fluids were originally meteoric water. Sulphur isotope ratios of sulphide and sulphate minerals, in association with the thermodynamic relations of the mineral assemblages, indicate that the sulphur was derived from at least two different sources; sedimentary sulphate and magmatic SO2, the relative importance of each varying from one deposit to another. Two types of hydrothermal systems are postulated for the formation of the epithermal deposits. During andesitic volcanism in the Miocene-early Pliocene, hydrothermal fluid convective cells were generated by heat from near surface small intrusive bodies of magma, whereas during rhyolitic volcanism in the late Miocene-Pleistocene the heat sources were larger plutons at greater depth. Porphyry copper deposits are associated with quartz diorite stocks intruded into Jurassic greywacke suite rocks and Miocene andesites. They are "diorite" model hypabyssal and volcanic types. The major minerals are quartz, pyrite, chalcopyrite and sphalerite. Additional minerals differ between the different deposits and define two contrasting geochemical environments of deposition, one characterised by low fS2, fO2 and Sigma S, indicated by the presence of pyrrhotite, and the other of moderate to high fS2, fO2 and Sigma S, indicated by the occurrence of bornite, magnetite or hematite. Associated hydrothermal alteration is generally propylitic although limited phyllic and "potassic" (defined by secondary biotite) types also occur in some deposits. Fluid inclusion and sulphur isotope studies of the Miners Head. porphyry copper deposit suggest that copper mineralisation occurred at a temperature of approximately 425 degrees C from fluids with apparent salinities up to.15.5 eq. wt. % NaCl and containing sulphur of magmatic origin, predominantly as H2S.</p>

Miniaturised Instrumentation for the Detection of Biosignatures in Ocean Worlds of the Solar System

This review of miniaturised instrumentation is motivated by the ongoing and forthcoming exploration of the confirmed, or candidate ocean worlds of the Solar System. It begins with a section on the evolution of instrumentation itself, ranging from the early efforts up to the current rich-heritage miniaturised mass spectrometers approved for missions to the Jovian system. The geochemistry of sulphur stable isotopes was introduced for life detection at the beginning of the present century. Miniaturised instruments allow the measurement of geochemical biosignatures with their underlying biogenic coding, which are more robust after death than cellular organic molecules. The role of known stable sulphur isotope fractionation by sulphate-reducing bacteria is discussed. Habitable ocean worlds are discussed, beginning with analogies from the first ocean world known in the Solar System that has always being available for scientific exploration, our own. Instrumentation can allow the search for biosignatures, not only on the icy Galilean moons, but also beyond. Observed sulphur fractionation on Earth suggests a testable “Sulphur Hypothesis”, namely throughout the Solar System chemoautotrophy, past or present, has left, or are leaving biosignatures codified in sulphur fractionations. A preliminary feasible test is provided with a discussion of a previously formulated “Sulphur Dilemma”: It was the Galileo mission that forced it upon us, when the Europan sulphur patches of non-ice surficial elements were discovered. Biogenic fractionations up to and beyond δ34S = −70‰ denote biogenic, rather than inorganic processes, which are measurable with the available high sensitivity miniaturised mass spectrometers. Finally, we comment on the long-term exploration of ocean worlds in the neighbourhood of the gas and ice giants.

Ore mineralogy, pyrite chemistry, and S isotope systematics of magmatic-hydrothermal Au mineralization associated with the Mooshla Intrusive Complex (MIC), Doyon-Bousquet-LaRonde mining camp, Abitibi greenstone belt, Québec

The Mooshla Intrusive Complex (MIC) is an Archean polyphase magmatic body located in the Doyon-Bousquet-LaRonde (DBL) mining camp of the Abitibi greenstone belt, Québec. The MIC is spatially associated with numerous gold (Au)-rich VMS, epizonal 'intrusion-related' Au-Cu vein systems, and shear zone-hosted (orogenic?) Au deposits. To elucidate genetic links between deposits and the MIC, mineralized samples from two of the epizonal 'intrusion-related' Au-Cu vein systems (Doyon and Grand Duc Au-Cu) have been characterized using a variety of analytical techniques. Preliminary results indicate gold (as electrum) from both deposits occurs relatively late in the systems as it is primarily observed along fractures in pyrite and gangue minerals. At Grand Duc gold appears to have formed syn- to post-crystallization relative to base metal sulphides (e.g. chalcopyrite, sphalerite, pyrrhotite), whereas base metal sulphides at Doyon are relatively rare. The accessory ore mineral assemblage at Doyon is relatively simple compared to Grand Duc, consisting of petzite (Ag3AuTe2), calaverite (AuTe2), and hessite (Ag2Te), while accessory ore minerals at Grand Duc are comprised of tellurobismuthite (Bi2Te3), volynskite (AgBiTe2), native Te, tsumoite (BiTe) or tetradymite (Bi2Te2S), altaite (PbTe), petzite, calaverite, and hessite. Pyrite trace element distribution maps from representative pyrite grains from Doyon and Grand Duc were collected and confirm petrographic observations that Au occurs relatively late. Pyrite from Doyon appears to have been initially trace-element poor, then became enriched in As, followed by the ore metal stage consisting of Au-Ag-Te-Bi-Pb-Cu enrichment and lastly a Co-Ni-Se(?) stage enrichment. Grand Duc pyrite is more complex with initial enrichments in Co-Se-As (Stage 1) followed by an increase in As-Co(?) concentrations (Stage 2). The ore metal stage (Stage 3) is indicated by another increase in As coupled with Au-Ag-Bi-Te-Sb-Pb-Ni-Cu-Zn-Sn-Cd-In enrichment. The final stage of pyrite growth (Stage 4) is represented by the same element assemblage as Stage 3 but at lower concentrations. Preliminary sulphur isotope data from Grand Duc indicates pyrite, pyrrhotite, and chalcopyrite all have similar delta-34S values (~1.5 � 1 permille) with no core-to-rim variations. Pyrite from Doyon has slightly higher delta-34S values (~2.5 � 1 permille) compared to Grand Duc but similarly does not show much core-to-rim variation. At Grand Duc, the occurrence of Au concentrating along the rim of pyrite grains and associated with an enrichment in As and other metals (Sb-Ag-Bi-Te) shares similarities with porphyry and epithermal deposits, and the overall metal association of Au with Te and Bi is a hallmark of other intrusion-related gold systems. The occurrence of the ore metal-rich rims on pyrite from Grand Duc could be related to fluid boiling which results in the destabilization of gold-bearing aqueous complexes. Pyrite from Doyon does not show this inferred boiling texture but shares characteristics of dissolution-reprecipitation processes, where metals in the pyrite lattice are dissolved and then reconcentrated into discrete mineral phases that commonly precipitate in voids and fractures created during pyrite dissolution.

Rare earth elements and stable sulphur (δ34s) isotope of baryte mineralization in Liji Area, Northern Benue trough, northeastern Nigeria

The Liji area lithologically consists of inliers of granite and pegmatite members of the Pan-African granitoids surrounded by Cretaceous sedimentary deposits of Bima, Yolde, Pindiga and Gombe Formations. Epigenetic fracture-filling baryte mineralization hosted by granite, pegmatite and Bima Sandstone were delineated, sampled and analyzed for rare-earth elements (REEs) and stable sulphur isotope geochemistry. The REEs of the distal (unaltered) rocks indicated normal values (26.15-36.81 ppm) before mineralization was marked by enrichment of light rare-earth elements (LREEs) (27.94 ppm) relative to the heavy rare-earth elements (HREEs) (5.34 ppm) and negative Eu anomalies typical of calc-alkaline granites of Pan-African age. The baryte separates were marked by enriched LREEs and depleted HREEs with pronounced positive Eu anomalies indicating the invasion and consequent deposition of baryte-rich hydrothermal fluid under oxidizing conditions in the N-S and E-W striking fractures. Stable sulphur isotope of the baryte gives values that ranged from 18.3 - 19.8o/oo CDT indicating that the source of sulphur is from ocean water and not from magmatic, fresh water and connate water sources from the nearby granite, pegmatite and sandstone. Keywords: Baryte, Mineralization, Hydrothermal, Liji, REE, Sulphur-Isotope.

Genesis of the Bagenheigeqier Pb–Zn skarn deposit in Inner Mongolia, NE China: constraints from fluid inclusions, isotope systematics and geochronology

Most skarns are found near the pluton or in lithologies containing at least some limestone. However, recent research has shown that neither a pluton nor limestone is necessarily required to form a skarn deposit. The newly discovered Bagenheigeqier Pb–Zn skarn deposit is located in NE China. The skarn and Pb–Zn orebodies occur in volcanic lithologies of the Baiyin’gaolao Formation and are controlled by NE–SW-trending faults. The nearest pluton is a granite porphyry, at a distance of 20–250 m from the orebodies. Five paragenetic stages at Bagenheigeqier are recognized: (I) skarn; (II) oxide; (III) early sulphide; (IV) late sulphide; and (V) late quartz–calcite. The fluid inclusions from stages II to V homogenized at temperatures of 402–452, 360–408, 274–319 and 167–212°C, respectively. The hydrogen and oxygen isotope compositions (δ18OH2O, –12.4‰ to +9.3‰; δDH2O, –156.5‰ to –99.1‰) indicate that the ore-fluids were primarily of magmatic origin, with the proportion of meteoric water increasing during the progression of ore formation. Sulphur isotope values (δ34SVCDT, 1.4–5.5‰), lead isotope values (206Pb/204Pb, 18.184–18.717; 207Pb/204Pb, 15.520–15.875; 208Pb/204Pb, 37.991–38.379) and the initial 187Os/188Os ratios of the pyrite (0.307 ± 0.06) suggest that the ore metals were derived from the granite porphyry and Baiyin’gaolao Formation. Re–Os dating of pyrite intergrown with galena and sphalerite yielded a well-constrained isochron age of 151.2 ± 4.7 Ma, which is coeval with the laser ablation – inductively coupled plasma – mass spectrometry zircon U–Pb age of 154 ± 1 Ma for the granite porphyry. The deposit was therefore formed during Late Jurassic time.