Sulphur isotope studies of the Mt Molloy,Dianne and O.K. stratiform sulphide deposits,Hodgkinson Province,North Queensland,Australia

Stratiform sulphide deposits which have been metamorphosed to lower greenschist facies occur within the Paleozoic strata of the Hodgkinson Province, northeast Queensland. Massive cupreous pyrite is ubiquitous and Mt Molloy and Dianne also have layered chalcopyrite-rich and sphalerite-rich lenses. Sulphide ³⁴S values for the mineralisation show a narrow spread, around 02030; at the Dianne and O.K. deposits, but a wider spread and an average several per mil higher at the Mt Molloy area. The minerals can not be used for geothermometry due to isotopic disequilibrium. However, metamorphic effects on the isotopic compositions appear not to have been significant. A decrease in temperature and contact of the ore fluid with sea water probably caused the precipitation of the ore minerals. A magmatic ore fluid with ³⁴S_S around 02030; predominated at the Dianne and OK deposits whereas the fluid at Mt Molloy mixed with sea water to acquire a higher ³⁴S_S value.     

Microfossil evidence for salinity events in the Holocene Coorong Lagoon,South Australia

Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.     

Reactive transport model of silicification at the Mount Isa copper deposit, Australia

A distinct feature of the world-class Mount Isa copper system is the presence of a massive silica body enveloping the chalcopyrite ore body in the Urquhart shale. Because silicification may be genetically linked to the copper mineralization, it is important to understand its formation. It can be shown by numerical simulations of reactive transport processes that both hydraulic head and buoyancy driven flow are capable of generating silicification patterns similar to the field example. Considering the physical conditions required to form the observed patterns we suggest, however, that head-driven flow rather than free thermal convection produced the silica body. Free convection requires very special conditions and only one of several possible scenarios reproduces the observed silicification whereas any of the tested forced flux scenario is capable of doing so.     

H,O,S and Pb isotope studies of uranium ore deposits in granitoid rocks of South China

Most altered clay minerals in uranium ore deposits in granites in the selected provinces of South China haveδ ¹⁸O _m values ranging from 6.22 to 7.24,δD_m from −60 to −70,δ ¹⁸O from +3.05 to −3.07, and from −20.2 to −37.5‰. Relative enrichment of³²S in the uranium ore deposits and greater variations in Pb isotopic composition of galenas from them show that uranium ores in the granites were formed in such a way that uranium in shallow-source granites had been mobilized by heated meteoric waters and then migrated to local favourable locations along great faults to form uranium ore deposits. Zhang Shaoli, Yang Wenjin, Tang Chunjing and Xu Wenxin did part of this work.     

The geology and genesis of the Tarcoola gold deposits,South Australia

The Tarcoola goldfield is located in the Gawler Craton in northwestern Eyre Peninsula, South Australia. The gold deposits are hosted in the Middle Proterozoic Tarcoola Formation, comprised of the fluviatile Peela Coglomerate Member, the shallow marine Fabian Quartzite Member, and the marine Sullivan Shale Member. Mineralization in the goldfield consists of north-northeast to north-northwest trending gold-bearing quartz veins with associated hematite, pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, electrum and gold. Adamellite in contact with the Tarcoola Formation has previously been included in the Middle Proterozoic Hiltaba Suite granitoids, on the basis of an apparent intrusive relationship with the Tarcoola Formation, and the gold-quartz veins were interpreted as being genetically related to the cooling pluton. However, detailed field and petrographic studies have demonstrated that the contact between the Tarcoola Formation and adamellite is a nonconformity. Hence, there is no genetic relationship between the mineralization and the adamellite. Oxygen isotope data indicate that an oreforming fluid, derived from convective circulation of meteoric or seawater, or from formation water, underwent isotope exchange with sediments of the Tarcoola Formation. A magmatic heat source for the hydrothermal system is suggested by the presence of intrusive igneous rocks, including dykes of aplite, quartz monzonite and microdiorite. Sulphur isotope characteristics of the mineralization can be explained by reduction of seawater sulphate or dissolution of disseminated sulphides in the sedimentary sequence. Metals were probably derived from rocks of the Tarcoola Formation. A complex paragenetic sequence involved deposition of minerals in several stages separated by episodes of fracturing. Fluid inclusions in quartz and fluorite show that deposition took place over a temperature range of about 340° to 110°C from a low salinity fluid. Analyses of chlorite coexisting with sulphide minerals suggest deposition of sulphides from about 300° to 170°C. Gold was transported as Au(HS) ₂ ^– and deposition appears to have coincided with a sudden decrease in fO₂ at around 260° to 250 °C.     

Two sulphur isotope provinces deduced from ores in the Mount Isa Eastern Succession,Australia

The sulphur isotopic characteristics of ore deposits in the Australian Mount Isa Eastern Succession are not well known, unlike those of the Western Succession. In this study new detailed analyses are provided for recently discovered Eastern Succession mineralisation, such as the Starra and Osborne BIF-hosted Cu-Au ores, the Dugald River sediment-hosted Pb-Zn prospect, and four vein-hosted Cloncurry-style Cu±Au deposits (Hampden, Mt Elliot/Swan, Mt Cobalt, and the Answer Mine). All of the deposits of the Eastern Succession have ³⁴S_sulphide between –8 and +9%., regardless of their genesis. Empirically a moderate (³⁴S range averaging close to 0%. characterises Starra-style Cu-Au and Pegmont Pb-Zn BIF ores, whereas shear and vein-style Cu mineralisation populations are tighter and do not average close to 0%. This is a particularly surprising result for Dugald River, where a larger isotopic variation more typical of stratiform sediment-hosted Pb-Zn ores in the region might have been expected. By comparison, Western Succession stratiform Pb-Zn and vein-style Cu deposits span a huge range of-15 to 51%. Large sulphur isotope ranges typify sulphate evaporite or organic sulphur-rich sedimentary successions. The lack of such variation in the Eastern Succession in turn suggests that primary evaporite sequences there were halite-dominated but sulphate-poor, and/or contained only limited volumes of organic-sulphur-rich sediment. Eastern Succession sequences were therefore less likely hosts for giant stratiform Pb-Zn deposits, because of their paucity of sulphur, although local sulphur sources permitted small deposits such as Dugald River to develop. Sedimentary conditions were more favourable for the development of sulphur-poor synsedimentary hydrothermal systems such as Starra, Osborne, and Pegmont, although sulphur isotope evidence is equivocal about the origin of these. Epigenetic deposits close to the Williams Batholith (Mt Dore, Hampden) owe their clustering around 0%. to their granitic fluid source.     

Biogeochemical studies at the Khetri copper deposits of Rajasthan,India

Several plants of the Khetri Copper Deposits of Rajasthan (India) accumulate very high levels of copper. The maximum concentration namely 394 ,μg/g (dry wt.) was found in the leaves of Talinum portulacifolium. Some other copper accumulators with the concentration of the metal in μg/g are: Tephrosia villosa (288), Rhus mysorensis (234) and Bouchea morubifolia (147). The respective biological absorption coefficients (copper in dried plant divided by copper in soil) for these four plants were 0.07, 1.35, 0.13 and 0.26, respectively. Leaves were found to be richer in copper than the stems. Copper levels in the leaves of Tephrosia villosa, Aerua tomentosa and Bouchea morubifolia showed a significant (linear) plant/soil relationship. Rhus mysorensis and Talinum protulacifolium showed absorption barriers at high soil copper concentrations, indicating limits to uptake in these two species.     

Pressure-temperature-fluid constraints for the Emmaville-Torrington emerald deposit, New South Wales, Australia: Fluid inclusion and stable isotope studies

The Emmaville-Torrington emeralds were first discovered in 1890 in quartz veins hosted within a Permian metasedimentary sequence, consisting of meta-siltstones, slates and quartzites intruded by pegmatite and aplite veins from the Moule Granite. The emerald deposit genesis is consistent with a typical granite-related emerald vein system. Emeralds from these veins display colour zonation alternating between emerald and clear beryl. Two fluid inclusion types are identified: three-phase (brine+vapour+halite) and two-phase (vapour+liquid) fluid inclusions. Fluid inclusion studies indicate the emeralds were precipitated from saline fluids ranging from approximately 33 mass percent NaCl equivalent. Formational pressures and temperatures of 350 to 400 °C and approximately 150 to 250 bars were derived from fluid inclusion and petrographic studies that also indicate emerald and beryl precipitation respectively from the liquid and vapour portions of a two-phase (boiling) system. The distinct colour zonations observed in the emerald from these deposits is the first recorded emerald locality which shows evidence of colour variation as a function of boiling. The primary three-phase and primary two-phase FITs are consistent with alternating chromium-rich ??striped?? colour banding. Alternating emerald zones with colourless beryl are due to chromium and vanadium partitioning in the liquid portion of the boiling system. The chemical variations observed at Emmaville-Torrington are similar to other colour zoned emeralds from other localities worldwide likely precipitated from a boiling system as well.     

Exploration potential of Cu isotope fractionation in porphyry copper deposits

We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ⁶⁵Cu‰ = ((⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_{NIST 976 standard}) − 1) ? 10³. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.     

Stratiform copper in the late proterozoic Boorloo delta,South Australia

The stratigraphic setting and geological environment of the Boorloo stratiform copper prospect is described. This prospect occurs in the Umberatana Group of the Adelaide Supergroup in the Willouran Ranges of South Australia. Stratiform copper mineralization occurs in stacked, braided, siliciclastic channels on the middle and distal portions of a late Proterozoic river-dominated delta. Comparison is made between this river-dominated delta copper system and the much larger river-dominated delta copper system of the Proterozoic Udokan deposit in the U. S. S. R. It is suggested that the traditional classifications of stratiform copper sensu strictu deposits as arenaceous-ore or oreshale can be viewed as dip-system or strike-system deposits respectively.     

Genesis of copper mineralisation,Myall Creek prospect,South Australia

The Myall Creek copper prospect is in unmetamorphosed carbonaceous dolosiltstone and sandstone at the base of the late Proterozoic (Adelaidean) Tapley Hill Formation. It contains disseminated, fine-grained chalcopyrite, zincian tennanite, bornite, chalcocite, pyrite, sphalerite and galena, and irregular to straight chalcopyrite-rich veinlets. Some ore minerals rim and/or partially replace pyrite or clastic grains. There is no evidence of hydrothermal activity. The ³⁴S_CDT values of pyrite and the other sulfides fall in the wide range –3.6 to +44.2. Dolomite in both mineralised and unmineralised samples has ¹³C_PDB values concentrated around –3, and ¹⁸O_SMOW values around +25. It is concluded that the mineralising fluids were near-neutral brines which leached metals from the basement and early Adelaidean rocks. They entered the Tapley Hill sediments at moderately low temperatures via permeable strata and faults. The metals were precipitated by biogenic H₂S, and also fixed by reaction with iron sulfides and, possibly, organic matter. Continuing ascent of brines into the mineralised strata caused breakdown of detrital feldspars and Fe-Ti oxides, and some solution-remobilisation of early-formed sulfides.     

Stable isotope study of carbonate sediments from the Coorong Area, South Australia

ABSTRACT
The mineralogy and isotope geochemistry of carbonate minerals in the Coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water. The different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral. In addition, the dolomite was not formed by simple solid state cation exchange.
The occurrence of two types of dolomite was shown by isotope analysis and SEM observations. The dolomite, which is isotopically light (δ¹³C = -1 to -2% 0 ; δ¹⁸O=+3 to +5%₀) and of fine grain size (˜ 0·5 μm) probably precipitated under the influence of evaporitically modified continental water. Coarser grained dolomite (up to 4 μm) is isotopically heavier (δ¹³C=+3 to +4%₀; δ¹⁸O=+5 to + 6%₀) contains Mg in excess of Ca and was formed in or close to equilibrium with atmospheric CO² probably by the dolomitization of aragonite.     

Proterozoic copper deposits in NW Queensland,Australia: Sulfur isotopic data

Sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in NW Queensland. A sulfur isotopic study of copper mineralization in dolomites at Paradise Valley and arenites at Mammoth has allowed the significance of such disequilibrium to be evaluated. Copper mineralization at Paradise Valley is characterized by a greater enrichment in ³⁴S, with δ³⁴S values often greater than +30‰, for both copper sulfides and associated syngenetic/diagneetic pyrite. At Mammoth, copper sulfides have isotopic compositions (δ³⁴S=?15.9 to ?0.3‰) transitional between disseminated syngenetic/diagenetic pyrite (δ³⁴S=?5.7 to ?1.7‰) and epigenetic vein pyrite (δ³⁴S=?17.9 to ?7.1‰) suggesting progressive reaction and replacement of syngenetic/diagenetic pyrite by a copper-bearing mineralizing fluid under oxidizing conditions. The isotopic data, within the constraints imposed by geological and geochemical factors, support a model of reaction between copper-bearing mineralizing fluids and pre-existing syngenetic/diagenetic pyrite for both the carbonate- and arenite-hosted deposits.     

A sulphur isotope study of the Broken Hill deposit,New South Wales,Australia

Sulphur isotopic compositions of sulphides within garnet-rich rocks and high-grade ore from the Broken Hill deposit, New South Wales, Australia, have been determined and show a range of values of –3.3 to +6.7 per mil. Thermochemical considerations, including the spread of values of ³⁴S, suggest that the deposit was derived from a mixed source of sulphur in which seawater, reduced by inorganic processes, mixed with magmatic sulphur or that sulphate from contemporaneous seawater was reduced biogenically at low temperatures. Thermochemical considerations also suggest that pyrrhotite formed by desulphidation of pyrite so that the original Fe-S-O assemblage was pyrite ± magnetite.³⁴S measurements show a broad range which is considered to be due to isotopic reequilibration during retrograde metamorphism and analytical and sampling technique. These data should not be used to indicate original temperatures of deposition or metamorphic temperatures associated with the various metamorphic events.     

中国北方金矿床铅同位素研究

本文着重讨论了我国北方地区几个主要金矿床的形成时代、矿源及其与铅同位素的关系。认为:①从内蒙到东部沿海(包括东北),金矿的形成时代从海西中期(311×10~6a)到燕山晚期(100×10~6a),并且大多数金矿与中生代的岩浆活动有关;②在由岩石铅(包括花岗岩和变质岩)和矿石铅同位素组成的~(207)Pb/~(204)pb-~(208)Pb/~(204)Pb图解上,矿石铅同位素组成更靠近花岗岩一端;③变质岩和花岗岩中的金具有很高的淋洗率,均可作为金矿的矿源岩石。     

Genesis of upper proterozoic stratabound copper mineralization,Kapunda, South Australia

Chalcopyrite-rich bedded and vein mineralization at Kapunda occurs in two locally developed dolosiltstone units within a sequence of generally darker-coloured, finer-grained calcmudstones and siltstones. The Mine Series accumulated in shallow water to supratidal, sabkha-like environments; there is no evidence for igneous activity in the region. Isotope data for bedded sulphides are characteristic of biological sulphate reduction in a restricted basin. It is likely that iron sulphides were produced initially, and that copper was introduced subsequently in mildly oxidizing, highly saline groundwaters, the influence of which is seen in the ¹³C-¹⁸O correlation for dolomite in the mineralized siltstones. Isotopic data support derivation of the veins from their host sediments, and this appears to have occurred before lithification.     

Electron spin resonance dating of the fossil deposits in the Naracoorte Caves,South Australia

The caves near Naracoorte, South Australia, contain one of the richest and most diverse fossil faunal assemblages on the Australian continent. Three sites were selected for electron spin resonance (ESR) dating because clastic, fossiliferous sediments were sandwiched between speleothem layers. This allows independent age control by highly precise thermal ionization mass‐spectrometry (TIMS) U‐series dating. We find that all ESR results agree within the constraints given by the U‐series dates, and allow further refinement of the age of the fauna analysed, indicating that most of the fauna in the large Victoria Cave Fossil Chamber is twice as old as reported previously. Our dating results, spanning from 280 to 500 ka for the Fossil Chamber, Victoria Cave, to about 125 ka for the Grant Hall, Victoria Cave, and 170 to 280 ka for the Fossil Chamber, Cathedral Cave, indicate little change, if any, in the megafaunal assemblage from the early Middle to the early Late Pleistocene. This changed dramatically after the last interglacial, when a large proportion of the megafauna suddenly disappeared. Copyright © 2001 John Wiley & Sons, Ltd.     

Changes in stable isotope ratios of metapelites and marbles during regional metamorphism,Mount Lofty Ranges,South Australia: implications for crustal scale fluid flow

The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, ¹⁸O values of normal metapelites decrease from 14–16 to as low as 9.0, while ¹⁸O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (¹⁸O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO₂ mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in ¹⁸O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x10⁹ moles/m² (10⁵ m³/m²). If fluid flow occurred over 10⁵–10⁶ years, estimated intrinsic permeabilities are 10^-20 to 10^-16m². Variations in ¹⁸O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO₂ values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both ¹⁸O and XCO₂ values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes     

Sulphur isotope geochemistry of carbonatites

Sulphur isotopic data for sulphides and barite from several carbonatites (Mountain Pass, Oka, Magnet Cove, Bearpaw Mountains, Phalabora) show that individual carbonatites have different mean sulphide or barite isotopic compositions which deviate from the meteoritic mean $\text{δ}{}^{34}\text{S(0‰)}$.Classification of carbonatites in terms of T,?O₂ and pH during formation of the sulphur-bearing assemblages indicates that with decreasing T and increasing relative ?O₂ the mean δ³⁴S sulphide becomes increasing negative relative to the mean magma δ³⁴S. Only barite-free high temperature carbonatites (Phalabora) in which the mean δ^34S sulphide approaches the mean magmaδ³⁴S as a consequence of the paucity of oxidized anionic sulphur species in the magma can be used to directly estimate the mean isotopic composition of the source material.Barites from the Mountain Pass carbonatite show an increase in δ³⁴S with sequence of intrusion of the carbonatite units; dolomitic carbonatite (mean δ³⁴S, + 5.4‰), calcitic carbonatite (+ 4.8%.), silicified carbonatite (+ 6.9‰), tabular carbonatite dikes (+ 8.7‰), mineralized shear zones (+ 9.5‰). Within each of these units a spread of 6.8%. is evident. Isotopic trends in this low temperature (300°C) carbonatite are evaluated by treating the system as a hydrothermal fluid. The observed isotopic variations can be explained by removal of large amounts of sulphur from a fluid whose mean δ³⁴S is 0 to + 1‰