Significance of phyllosilicate mineralogy and mineral chemistry in an epithermal environment. Insights from the palai-islica Au-Cu deposit (Almería, SE Spain)

Abstract

X-ray diffraction, optical and electronic microscopy (scanning and transmitted), electron microprobe and Fourier transform infra red spectroscopy has been used to study phyllosilicates in the Palai-Islica Au-Cu epithermal, volcanichosted deposit, in order to link phyllosilicate mineralogy and mineral chemistry to ore genesis. Thus, different phyllosilicate assemblages characterize two types of mineralization, and related hydrothermal alteration. Chlorite and mica appear in polymetallic quartz veins with sulfides, and in the related chloritic and sericitic hydrothermal alteration. These minerals have notable textural and chemical differences (i.e. Fe/(Fe+Mg), Si and Al in chlorite and illitic and phengitic components in mica) amongst veins and altered rocks, revealing different genetic conditions. These chemical features also distinguish propylitic and regional, non ore-1 related, low-temperature alteration. Hot hydrothermal fluids of near-neutral pH are responsible for vein mineralization and alteration. Illite, interstratified illite-smectite, kaolinite and pyrophyllite are characteristic, with a distribution pattern by zones, for the intermediate argillic and advanced argillic alteration around areas of silicification. In the latter, native gold appears associated to interstratified illitesmectite, suggesting a relatively low temperature formation. Hot, low-pH fluids are responsible for this mineralization and alteration assemblage. The present study contributes to epithermal models showing the coexistence of two different alteration styles in the same hydrothermal system.

From deep to shallow fluid reservoirs: evolution of fluid sources during exhumation of the Sierra Almagrera, Betic Cordillera, Spain

“…; Carrillo‐Rosúa et al . ). Ba‐Ag mineralization is found in sedimentary rocks, close to high‐K calc‐alkaline and shoshonitic volcanics within the Vera Basin (Alvado ; Martínez‐Frías ).…”

“…1). Epithermal ore deposits are hosted by intermediate to acid volcanics ranging in age from 12 to 10 Ma; these deposits are found in a number of different mining districts, for example Zn-Pb-Cu(-Ag-Au) at San Jos e (Demoustier et al 1998;Esteban-Arispe et al 2009), Au(-Cu-Te-Sn) at Rodalquilar (Arribas et al 1995) and Cu-Au-Ag at Carboneras (Morales Ruano et al 2000;Carrillo-Ros ua et al 2009). Ba-Ag mineralization is found in sedimentary rocks, close to high-K calcalkaline and shoshonitic volcanics within the Vera Basin (Alvado 1986;Mart ınez-Fr ıas 1998).…”

Kaolinization — a tool to unravel the formation and unroofing of the Pleystein pegmatite–aplite system (SE Germany)

“…They come into existence during the waning stages of volcanism, producing mainly felsic volcanic and volcaniclastic rocks affected by an acid-type alteration of epithermal deposits (Dill et al, 1995(Dill et al, , 1997Cravero et al, 2001;Carrillo-Rosúa et al, 2009;Marfil et al, 2010;Kadir and Erkoyun, 2013). Mineralogically, they are characterized by Na-and K alunites and APS minerals,…”

Petrography and Geochemistry of Hydrothermal Alteration in the Low-Sulfidation Epithermal Kestanelik Au Deposit, Biga Peninsula, NW Turkey

“…Compared to the wealth published in the literature regarding the research into the origin of epithermal Au-Ag deposits, there are very few detailed clay mineralogy studies on the alteration zones of epithermal deposits [28][29][30][31][32][33][34]. In a mineralogical study on the argillic alteration zone in the low-sulfidation epithermal type Ovacık-Bergama Au-Ag deposit, it was noted that telescoping resulted in four episodes of alteration [28].…”