Jiajun Liu

Gold-telluride-sulfide association in the Sandaowanzi epithermal Au-Ag-Te deposit, NE China: implications for phase equilibrium and physicochemical conditions

The Sandaowanzi gold-telluride deposit, with a total reserve of u2009≥u200925xa0t of Au and an average grade of 15xa0g/t, is located in the Great Hinggan Range Metallogenic Belt in NE China. This deposit is the first reported case of a dominantly Au (±Ag)-telluride deposit in this area and it reveals highly economic bonanza Au- and Ag-telluride ores. Ore bodies principally occur in quartz veins and stockworks and minor in disseminations hosted by trachyandesites and andesitic breccias. Four paragenetic stages of mineralization are identified, demonstrating an early deposition of sulfides and subsequent precipitation of tellurides, which are mainly composed by petzite, sylvanite and to a lesser extent, hessite, calaverite, altaite, unnamed telluride (Au1.8Ag0.2Te), krennerite, empressite, stützite and coloradoite. Abundant telluride assemblages identified from Sandaowanzi ores are mostly attributed to breakdown of early tellurium-bearing phases (i.e., γ- and χ-phases) during cooling. The deposition of substantial Au-Ag-Te minerals are constructed under physicochemical conditions of Tu2009=u2009240 to 280xa0°C, pHu2009=u20094.39 to 5.64, logfO2u2009=–44.8 to –41.8, logfTe2u2009=–9.75 to –9.43, logαAu+(aq)/αAg+(aq)u2009=u2009−6.87 to –6.56, and gold is mostly scavenged from a HTe−-dominant ore-forming fluid. The unusually high Te concentrations in the Sandaowanzi epithermal system are likely attributed to alkaline to calc-alkaline magmatic degassing.

Geochemical characteristics of rare earth elements and their implications for the Huachanggou gold deposit in Shaanxi Province, China

Abstract The Huachanggou gold deposit is located in the south part of the Mian-Lue suture zone in the Qinling orogenic belt. Rare earth element (REE) concentrations determined by ICP-MS are shown to characterize the ore samples and their wall rocks in three ore zones in order to reveal the origin of ore-forming materials and fluid. In AuI, REE chondrite normalized patterns of ore are similar to those of ore-controlling spilite; the ore-forming materials originated from deep magma, and magmatic activity offered main hydrothermal source for gold mineralization. The REE characteristics of AuII and AuIII are similar, and most of the ore samples are similar with the wall rocks. The ore-forming fluids of AuII and AuIII were metamorphic hydrothermal fluids which had extracted ore-forming materials part from the wall rocks, and part from the spilite in AuI.

Fluid inclusion and isotope geochemistry of the Yangla copper deposit, Yunnan, China

The Yangla copper deposit, with Cu reserves of 1.2 Mt, is located between a series of thrust faults in the Jinshajiang–Lancangjiang–Nujiang region, Yunnan, China, and has been mined since 2007. Fluid inclusion trapping conditions ranged from 1.32 to 2.10xa0kbar at 373–409xa0°C. Laser Raman spectroscopy confirms that the vapour phase in these inclusions consists of CO2, CH4, N2 and H2O. The gas phases in the inclusions are H2O and CO2, with minor amounts of N2, O2, CO, CH4, C2H2, C2H4, and C2H6. Within the liquid phase, the main cations are Ca2+ and Na+ while the main anions are SO42− and Cl−. The oxygen and hydrogen isotope compositions of the ore-forming fluids (−3.05‰u2009≤u2009δ18OH2Ou2009≤u20092.5‰; −100‰u2009≤u2009δDu2009≤u2009−120‰) indicate that they were derived from magma and evolved by mixing with local meteoric water. The δ34S values of sulfides range from −4.20‰ to 1.85‰(average on −0.85‰), supporting a magmatic origin. Five molybdenite samples taken from the copper deposit yield a well-constrained 187Re–187Os isochron age of 232.8u2009±u20092.4xa0Ma. Given that the Yangla granodiorite formed between 235.6u2009±u20091.2xa0Ma and 234.1u2009±u20091.2xa0Ma, the Cu metallogenesis is slightly younger than the crystallization age of the parent magma. A tectonic model that combines hydrothermal fluid flow and isotope compositions is proposed to explain the formation of the Yangla copper deposit. At first, westward subduction of the Jinshajiang Oceanic Plate in the Early Permian resulted in the development of a series of thrust faults. This was accompanied by fractional melting beneath the overriding plate, triggering magma ascent and extensive volcanism. The thrust faults, which were then placed under tension during a change in tectonic mode from compression to extension in the Late Triassic, formed favorable pathways for the magmatic ore-forming fluids. These fluids precipitated copper-sulfides to form the Yangla deposit.