Geology, geochronology, fluid inclusions, and isotope geochemistry of the Rodalquilar gold alunite deposit, Spain

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...

Mineralogical Distribution of Germanium, Gallium and Indium at the Mt Carlton High-Sulfidation Epithermal Deposit, NE Australia, and Comparison with Similar Deposits Worldwide

“…We used two separate analytical protocols for sulfates/silicates and sulfides/sulfosalts, respectively. For alunite, barite and dickite, the collected analytes were 27 Al, 31 P, 44 Ca, 49 Ti, 53 Cr, 55 Mn, 57 Fe, 65 Cu, 66 Zn, 71 Ga, 72 Ge, 75 As, 77 Se, 85 Rb, 88 Sr, 98 Mo, 107 Ag, 115 In, 118 Sn, 121 Sb, 137 Ba, 139 La, 140 Ce, 197 Au, 208 Pb, 209 Bi, 232 Th and 238 U. The internal standard isotopes used for data reduction were 27 Al (alunite and dickite) and 137 Ba (barite), based on contents confirmed previously by WDS.…”

“…NIST-SRM-610 [51] was used as a bracketing external standard, and GSE-1G and GSD-1G [52] were analyzed as secondary standards to evaluate accuracy. For enargite, sphalerite, pyrite and galena, the collected analytes were 51 V, 52 Cr, 55 Mn, 57 Fe, 59 Co, 60 Ni, 65 Cu, 66 Zn, 71 Ga, 72 Ge, 75 As, 77 Se, 95 Mo, 107 Ag, 114 Cd, 115 In, 118 Sn, 121 Sb, 125 Te, 197 Au, 202 Hg, 205 Tl, 208 Pb and 209 Bi. USGS Mass-1 [53] was used as a bracketing external standard, and NIST-SRM-610, GSE-1G and GSD-1G were used as secondary standards.…”

“…USGS Mass-1 [53] was used as a bracketing external standard, and NIST-SRM-610, GSE-1G and GSD-1G were used as secondary standards. 65 Cu (enargite), 66 Zn (sphalerite), 57 Fe (pyrite) and 208 Pb (galena) were used as the internal standard isotopes, based on contents confirmed previously by WDS.…”

“…The trace element signatures for enargite from Mt Carlton in part corroborate the trends observed at Far Southeast-Lepanto, suggesting that this method may have some potential as a vectoring tool for exploration in the porphyry-epithermal environment. Furthermore, at the Rodalquilar HS deposit, the presence of anomalous Sn concentrations (high enough to form Sn-bearing minerals such as cassiterite (wood tin), colusite or rodalquilarite; [66]) was considered to be a prospective guide to high Au grade mineralized structures [67].…”

Sentinel-2 for Mapping Iron Absorption Feature Parameters

“…These rocks have been extensively altered to form an assemblage of high to low temperature grade metamorphic minerals, such as Silica, Alunite, Kaolinite, Montmorillonite and Chlorite. The geology of the area is described in Arribas et al [38], while several remote sensing studies were conducted at this site as well [4,[39][40][41][42].…”