No abstract

The Rodalquilar epithermal Au alunite deposit occurs within the Rodalquilar caldera complex in the Miocene Cabo de Gata volcanic field in southeastern Spain. The Rodalquilar caldera formed by eruption of the rhyolitic Cinto ash-flow tuff at about 11 Ma; continued resurgence of the core of the caldera resulted in structural doming and was followed by emplacement of large ring domes, eruption of the Lfizaras ash-flow tuff, and development of the smaller, nested Lomilla caldera. Hydrothermal circulation associated with the emplacement of shallow hornblende andesitic intrusions late in the evolution of the caldera led to formation of the epithermal deposits along fractures related to multistage caldera collapse and resurgence.Ore deposits within the Rodalquilar caldera complex consist of low-sulfidation Pb-Zn-(Cu-Ag-Au) quartz veins and the economically most important high-sulfidation Au-(Cu-Te-Sn) ores. The latter are enclosed in areas of acid sulfate alteration present on the east margin of the Lomilla caldera. Drilling indicates that hydrothermally altered rocks are present to depths of >900 m, with a gradational change with depth from silicic, to advanced argillic, to intermediate argillic, to sericitic zones; an envelope of propylitic alteration surrounds these zones. The sericitic zone is present at depths >400 m and occurs under the advanced argillic (stage i alunite, diaspore, zunyite, pyrophyllite) and silicic (vuggy silica and massive silicified rock) zones, which are well developed to present depths of •300 and 100 m, respectively. Vuggy silica and massive silicified rock are structurally controlled and spatially related to the Au deposits. K/Ar dating of stage i alunite and hydrothermal illitc indicates an age of mineralization of about 10.4 Ma.The results of paragenetic, fluid inclusion, and stable isotope studies indicate an evolution of the hydrothermal system, consisting of an early period of acidic wall-rock alteration and a late period of Au mineralization. A significant magmatic fluid component was present throughout, contributing acidity in the form of H2SO4 and HC1. Salinities in some samples of deep, hot (>400øC) fluids exceeded 40 wt percent NaC1 equiv, consistent with the presence of a magmatic brine. In addition, the O and H isotope ratios of hypogene alteration minerals (alunite, kaolinitc, sericite, and hydrothermal quartz) indicate that hydrothermal fluids (6•SO = 7 ___ 3%0, 6D = -20 ___ 10%o) during the main period of wall-rock alteration were dominantly magmatic in origin. The 634Szs was •9 per mil and H2S/SO4 of the bulk hydrothermal system during acidic alteration was •5. The 634S values of stage 1 alunite (22.3-31.0%o) and pyrite (0.3-8.0%0) in the advanced argillic zone reflect isotopic equilibrium between sulfate and sulfide at T --220 ø to 330øC, with the lower values corresponding with present-day surface samples. * Present address: Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305 Japan. 0361-0128/95/1704/795-2854.00 795 796 ,4RRIB,•S, JR. ET ,•L. Gold mineralization extend...

Determining the chemical speciation of mercury in contaminated mining and industrial environments is essential for predicting its solubility, transport behavior, and potential bioavailability as well as for designing effective remediation strategies. In this study, two techniques for determining Hg speciation--X-ray absorption fine structure (XAFS) spectroscopy and sequential chemical extractions (SCE)--are independently applied to a set of samples with Hg concentrations ranging from 132 to 7539 mg/kg to determine if the two techniques provide comparable Hg speciation results. Generally, the proportions of insoluble HgS (cinnabar, metacinnabar) and HgSe identified by XAFS correlate well with the proportion of Hg removed in the aqua regia extraction demonstrated to remove HgS and HgSe. Statistically significant (>10%) differences are observed however in samples containing more soluble Hg-containing phases (HgCl2, HgO, Hg3S2O4). Such differences may be related to matrix, particle size, or crystallinity effects, which could affect the apparent solubility of Hg phases present. In more highly concentrated samples, microscopy techniques can help characterize the Hg-bearing species in complex multiphase natural samples.

Mercury deposits are globally distributed in 26 mercury mineral belts. Three types of mercury deposits occur in these belts: silica-carbonate, hot-spring, and Almaden. Mercury is also produced as a by-product from several types of gold-silver and massive sulfide deposits, which account for 5% of the world's production. Other types of mineral deposits can be enriched in mercury and mercury phases present are dependent on deposit type. During processing of mercury ores, secondary mercury phases form and accumulate in mine wastes. These phases are more soluble than cinnabar, the primary ore mineral, and cause mercury deposits to impact the environment more so than other types of ore deposits enriched in mercury. Release and transport of mercury from mine wastes occur primarily as mercury-enriched particles and colloids. Production from mercury deposits has decreased because of environmental concerns, but by-product production from other mercuryenriched mineral deposits remains important.

No abstract

No abstract

No abstract

No abstract