Sulphur-isotope and elemental geochemistry studies of the Hemlo gold mineralization, Ontario: sources of sulphur and implications for the mineralization process

1991 ◽  
Vol 28 (1) ◽  
pp. 13-25 ◽  
Author(s):  
H. G. Thode ◽  
T. Ding ◽  
J. H. Crocket
Keyword(s):  
Gold Mineralization ◽  
Country Rock ◽  
Minor Element ◽  
Sulphur Isotope ◽  
Isotopic Compositions ◽  
Heavy Rare Earth Elements ◽  
Wide Scale ◽  
Isotope Equilibrium ◽  
End Members ◽  
Hydrothermal Sulphide

A study of the sulphur-isotope and minor-element composition of gold ores and country rock from the Hemlo deposit, Ontario, has been carried out on 10 drill cores from the mineralization zone and two occurrences of stratiform barite west of Hemlo. The work confirms that Mo, As, and Sb correlate strongly with Au, whereas Ba, and by inference barite, does not. A preferential association of heavy rare-earth elements with higher grades of Au was also established. The isotopic compositions of barite and pyrite reflect a deposit-wide thermal equilibration at 504 °C. Whole-rock sulphur isotopic compositions can be modelled as a mix of sulphate and sulphide end members, the former marked by a relatively constant isotopic composition of roughly 10‰ and the latter by variable and negative isotopic compositions in mineralized zones.These isotopic characteristics are interpreted as the result of (i) preliminary fluid–rock reactions in which some isotope exchange between sedimentary barite and hydrothermal sulphide has occurred and (ii) a later stage metamorphic event in which sulphur-isotope equilibrium is established between the precipitated, distinctly isotopically light pyrite and bedded barite. These two fractionation events, separated in space and time, are required to explain both the variable and distinctly negative δ34S values observed for the pyrite in the Hemlo ores (−15.9 to +1.0%o) and the uniform Δδ34S value of 12.7 ± 1‰ obtained for the coexisting barite and pyrite pairs, in widely different proportions on a deposit-wide scale. Both the production of light isotopic sulphide and the later precipitation of Au are thought to have been influenced by an increase in fluid[Formula: see text].

scholarly journals Investigations of the photochemical isotope equilibrium between O<sub>2</sub>, CO<sub>2</sub> and O<sub>3</sub>

2006 ◽  
Vol 6 (4) ◽  
pp. 7869-7904
Author(s):  
R. Shaheen ◽  
C. Janssen ◽  
T. Röckmann
Keyword(s):  
Room Temperature ◽  
Strong Dependence ◽  
General Relation ◽  
Oxygen Isotopic Composition ◽  
Isotopic Compositions ◽  
Dependent Relationship ◽  
Dependent Relation ◽  
Oxygen Isotopic ◽  
Isotope Equilibrium ◽  
Mass Dependent

Abstract. Contrary to tropospheric CO2 whose oxygen isotopic composition follows a standard mass dependent relationship, i.e. δ17O~0.5 δ18O, stratospheric CO2 is preferentially enriched in 17O, leading to a strikingly different relation with δ17O~1.7δ18O. The isotope anomaly is likely inherited from O3 via photolytically produced O(1D) that undergoes isotope exchange with CO2 and the anomaly may well serve as a tracer of stratospheric chemistry if details of the exchange mechanism are understood. We have studied the photochemical isotope equilibrium in UV-irradiated O2-CO2 and O3-CO2 mixtures to quantify the transfer of the anomaly from O3 to CO2 at room temperature. By following the time evolution of the oxygen isotopic compositions of CO2 and O2 under varying initial isotopic compositions of both, O2/O3 and CO2, the isotope equilibria between the two reservoirs were determined. A very strong dependence of the isotope equilibrium on the O2/CO2-ratio was established. Equilibrium enrichments of 17O and 18O in CO2 relative to O2 diminish with increasing CO2 content, and this reduction in the equilibrium enrichments does not follow a standard mass dependent relation. When molecular oxygen exceeds the amount of CO2 by a factor of about 20, 17O and 18O in equilibrated CO2 are enriched by (142±4) and (146±4), respectively, at room temperature and at a pressure of 225 hPa, independent of the initial isotopic compositions of CO2 and O2 or O3. From these findings we derive a simple and general relation between the starting isotopic compositions and amounts of O2 and CO2 and the observed slope in a three oxygen isotope diagram. Predictions from this relation are compared with published laboratory and atmospheric data.

The geochemical evolution of Nb–Ta–Sn oxides from pegmatites of the Cape Cross–Uis pegmatite belt, Namibia

2018 ◽  
Vol 83 (02) ◽  
pp. 161-179 ◽  
Author(s):  
Warrick C. Fuchsloch ◽  
Paul A. M. Nex ◽  
Judith A. Kinnaird
Keyword(s):  
Country Rock ◽  
Minor Element ◽  
Aqueous Fluid ◽  
Geochemical Evolution ◽  
Rare Element ◽  
Fractionation Process ◽  
North Central ◽  
Mineral Inclusions ◽  
Late Stages ◽  
Zonation Patterns

AbstractThe Cape Cross–Uis pegmatite belt, Damara Orogen, north-central Namibia hosts multiple Ta–Nb- and Sn-oxide-bearing pegmatites. Columbite-group minerals, tapiolite, cassiterite and minor ixiolite and wodginite occur in abundance within pegmatites and display various compositional and internal structural mineralogical variations. Ta–Nb oxides display various zonation patterns indicative of multiple crystallisation phases, whereas cassiterite is dominantly homogeneous with minor euhedral columbite-group mineral inclusions. Ta–Nb oxides are mostly rich in Fe, with fractionation patterns in the columbite quadrilateral being sub parallel to the Ta/(Ta + Nb) axis; increasing Ta/(Ta + Nb) with little change in Mn/(Mn + Fe), which is consistent with classical trends in beryl-to-spodumene rare-element pegmatites. In addition, these trends suggest that co-crystallising minerals compete with Ta–Nb oxides for elements such as Mn, preventing Ta–Nb oxides from attaining Mn-rich compositions during the fractionation process. Cassiterite shows similar fractionation patterns with Fe &gt; Mn and notable increases in the Ta content. Minor-element substitution in Ta–Nb oxides shows sharp decreases with increasing fractionation supporting the hypothesis that newly stabilised co-occurring minerals compete with columbite-group minerals for certain elements. Tapiolite shows the same minor-element trend, however, only for Sn and Ti suggesting cassiterite was a dominant competing mineral. Although crystallisation of Ta–Nb oxides from an aqueous fluid at the late-stages of pegmatite genesis is highly debated, significantly elevated Ta contents in metasomatised country rock, compared to unaltered country rock, may give new insight, suggesting that Ta may indeed partition into, and be transported by, an exsolved aqueous fluid. However, further studies of the country rock metasomatic contacts are required as currently the dataset is limited. The degree of fractionation as depicted by Ta–Nb and Sn oxides within pegmatites, indicate that a zonation from primitive to evolved pegmatites surrounding granites is not present and that pegmatites are probably not related to granites in the typical parent–daughter relationship.

Relationship between δ18O and minor element composition of Terebratalia transversa

2007 ◽  
Vol 98 (3-4) ◽  
pp. 443-449 ◽  
Author(s):  
Maggie Cusack ◽  
David Parkinson ◽  
Alberto Pérez-Huerta ◽  
Jennifer England ◽  
Gordon B. Curry ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Isotope Composition ◽  
Seawater Temperature ◽  
Minor Element ◽  
Oxygen Isotope Composition ◽  
Secondary Layer ◽  
Vital Effects ◽  
Stable Oxygen ◽  
Temperature Proxy ◽  
Isotope Equilibrium

ABSTRACTWith their extensive fossil record and shells of stable low-Mg calcite, rhynchonelliform brachiopods are attractive sources of climate information via seawater temperature proxies such as stable oxygen isotope composition. In Terebratalia transversa (Sowerby) there is a progression towards oxygen isotope equilibrium in the calcite of the innermost secondary layer. This study confirms the lack of any vital effects influencing oxygen isotope composition of T. transversa, even in specialised areas of the innermost secondary layer. Calcite Mg/Ca ratio is another potential seawater temperature proxy, that has the advantage of not being influenced by salinity. Mg concentrations measured by electron microprobe analyses indicate that there is no concomitant decrease in Mg concentration towards the inner secondary layer, associated with the progressive shift towards oxygen isotope equilibrium. Mg distribution is heterogeneous throughout the shell and correlates with that of sulphur, which may be a proxy for organic components, suggesting that some of the Mg may not be in the calcite lattice. It is essential therefore, to determine the chemical environment of the magnesium ions to avoid any erroneous temperature extrapolations in brachiopods or any other calcite biomineral.

Inferences of lithospheric evolution in Italy from Pb isotopic compositions in northern Apennine cherts

1985 ◽  
Vol 22 (9) ◽  
pp. 1370-1373 ◽  
Author(s):  
R. Vollmer
Keyword(s):  
Upper Jurassic ◽  
Isotopic Signature ◽  
Northern Apennines ◽  
Pb Isotope ◽  
Sea Floor ◽  
Isotope Data ◽  
Isotopic Compositions ◽  
End Members ◽  
Metasomatized Mantle ◽  
Lithospheric Evolution

Pb isotope data by Barrett on Upper Jurassic cherts and associated ophiolites in the northern Apennines form a mixing trend with only two end members. Oblique secondary trends in the data are most likely an effect of radiogenic growth since the Jurassic and not due to multiple end members as proposed by Thorpe in his criticism of Barrett. Implications of these data for the evolution of the lithosphere in this region have not been previously discussed: (1) the distinct Pb isotopic signature of the chert end member is shared by the Pb in the Cenozoic Tuscan anatectic magmas, which suggests the same crustal provenance for both leads, and (2) the Jurassic sea-floor basalts constrain the age of anomalous metasomatized mantle now underlying most of Italy to less than 140 Ma.

Timing between granitoid emplacement and associated gold mineralization: examples from the ca. 2.7 Ga Harare–Shamva greenstone belt, northern Zimbabwe

1996 ◽  
Vol 33 (7) ◽  
pp. 981-992 ◽  
Author(s):  
M. L. Vinyu ◽  
H. A. Jelsma ◽  
R. Frei
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Time Frame ◽  
Gold Deposits ◽  
Isotopic Signatures ◽  
Ore Minerals ◽  
Granitoid Emplacement ◽  
Wide Scale ◽  
Temporal And Spatial ◽  
Favorable Conditions

Structurally controlled Late Archaean gold mineralizations associated with felsic plutons in the Harare–Shamva greenstone belt, Zimbabwe, are synchronous with the emplacement of their hosts. The ages of these mineralizations are identical to those reported from other mesothermal gold deposits elsewhere in the Zimbabwe Craton. The Pb and Nd isotopic signatures of the host plutons are compatible with a direct mantle or a short crustal residence period for the protoliths to the host intrusions. The coincidence of the Pb-isotope data from ore minerals with the whole-rock trends (errorchrons) of their host intrusives strongly suggests that the gold could have a magmatic, rather than a metamorphic, source. There is no evidence from the Pb isotopes of significant involvement of older basement in the genesis of gold deposits associated with felsic intrusions in the Harare–Shamva greenstone belt. On a craton-wide scale, the time frame around 2.65 Ga represents a period of significant crustal growth (through addition of mantle-derived magma), deformation, and metamorphism. The temporal and spatial coincidence of these three parameters has created favorable conditions for the emplacement of the largest class of Archaean gold mineralizations that are currently known in the country.

Fluid inclusion and stable isotope constraints on the origin of Wernecke Breccia and associated iron oxide – copper – gold mineralization, Yukon

2011 ◽  
Vol 48 (10) ◽  
pp. 1425-1445 ◽  
Author(s):  
Julie A. Hunt ◽  
Tim Baker ◽  
James Cleverley ◽  
Garry J. Davidson ◽  
Anthony E. Fallick ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Fluid Inclusion ◽  
Gold Mineralization ◽  
Fluid Pressure ◽  
Yukon Territory ◽  
Metasedimentary Rocks ◽  
Isotopic Compositions ◽  
Copper Gold ◽  
Oxygen Isotopic ◽  
Hydrothermal Sulfides

Iron oxide – Cu ± Au ± U ± Co (IOCG) mineralization is associated with numerous Proterozoic breccia bodies, collectively known as Wernecke Breccia, in Yukon Territory, Canada. Multiphase breccia zones occur in areas underlain by Paleoproterozoic Wernecke Supergroup metasedimentary rocks and are associated with widespread sodic, potassic, and carbonate alteration assemblages. Fluid inclusion data indicate syn-breccia fluids were hot (185–350 °C) saline (24–42 wt.% NaCl equivalent) NaCl–CaCl2–H2O brines. Estimates of fluid pressure vary from 0.4 to 2.4 kbar (1 kbar = 100 MPa). Carbon and oxygen isotopic compositions of breccia-related carbonates range from ~–11‰ to +1.5‰ (Pee Dee belemnite (PDB)) and –2‰ to 20‰ (Vienna standard mean ocean water (V-SMOW); δ18Owater ~–8‰ to +15‰), respectively. δ13C and δ18O values for host Wernecke Supergroup limestone/dolostone vary from ~–2‰ to 1.6‰ and 12‰ to 25‰, respectively. Sulfur isotopic compositions of hydrothermal sulfides and sulfate vary from ~–12‰ to +13‰ and +8‰ to +17‰ (Cañon Diablo Troilite (CDT)), respectively. Syn-breccia biotite, muscovite, and actinolite have δD and δ18O values of ~–141‰ to –18‰ and +7‰ to +12‰ (V-SMOW; δ18Owater ~7‰ to 11‰), respectively. The Wernecke Breccias and the associated IOCG mineralization appear to have formed from largely nonmagmatic fluids — based on isotopic, fluid inclusion, and geological data. The emerging hypothesis is that periodic overpressuring of dominantly formational/metamorphic water led to repeated brecciation and mineral precipitation. The weight of overlying sedimentary rocks led to elevated fluid temperatures and pressures; fluid flow may have been driven by tectonics and (or) gravity with metals scavenged from host strata.

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