HR: 1340h
AN: V13B-1464    [Abstracts]
TI: Metallogeny of The Sierra de Guanajuato Range, Central M\'{e}xico
AU: * PEDRO F., Z D
EM: pzarate@ccip.udg.mx
AF: UNIVERSIDAD DE GUADALAJARA-CUCEI, AP. POSTAL 4-021, GUADALAJARA, JAL 44410 Mexico
AB: The Sierra de Guanajuato Range ({\bf SGR}), trending N315$\deg$ at Central M\'{e}xico, is an orographic feature extending over a distance of 80 km. {\bf SGR} comprises three well defined lithostratigraphic units: {\bf (1)} a cretaceous basement including an arc-derived terrane named Guanajuato Arc (GA) made of gabbro, diorite and basaltic pillowed lava, and volcano-sedimentary rocks belonging to Arperos fore-arc basin which are geochemically anomalous in Au (0.15 ppm), Ag (3 ppm), Cu (40 ppm), Pb (50 ppm) and Zn (15 ppm); {\bf (2)} Early Tertiary intrusive rocks, e.g., Comanja Granite which is affected by the presence of tourmalinized (sch\"{o}rl) aplito-pegmatite dykes mineralized with rare earths elements, and {\bf (3)} Eocene redbeds (1,500-2000 m) and Oligocene-Miocene volcanics cover. The metallogeny of the {\bf SGR} shows a multiple origin in time and space: volcano-sedimentary, granitic and volcanic, being possible to define three metallogenic epochs: cretaceous, paleocene and oligocene. {\bf Cretaceous epoch} includes: {\bf (a)} volcanogenic massive sulphide deposits ({\bf VMS}) of bimodal-siliclastic type belonging to Le\'{o}n-Guanajuato district; wallrock of {\bf VMS} is made of felsic-internediate volcanics and black argillite; at Los Gavilanes deposit paragenesis is next: chalcopyrite $>$ sphalerite $>$ galena, pyrite $>$ pyrrhotite $>$ marcasite; grade is as follows: Au: .02-.07 g/t; Ag: 157-18.5 g/t; Cu: 2.24-0.81%, Pb: 4.16-0.03%; Zn: 10.35-3.02 %; {\bf (b)} lens-shaped stratiform bodies of massive pyrite (i. ex., San Ignacio prospect; $\sim$ 4,000 ton) of exhalative-sedimentary origin with chalcopyrite and sphalerite microveins. {\bf Paleocene epoch} includes both quartz-cordierite-sanidine veins and replacement bodies of hydrothermal metamorphic filliation (W +Se-Bi, Pb, Zn, Cu), and pyrometasomatic bodies [Cu, Pb, Zn (Ag), W] which genetically are linked to Comanja Granite emplacement. The wallrock at El Maguey mine (35,000 ton; 0.6% WO3) is made of hornfel and the vein (1.8-3.2m width) has a banding structure made of : \{quartz & K-feldspar\}, \{(sch\"{o}rl) & specular hematite\} and epidote alternating bands; ore minerals are scheelite and tetradymite. {\bf Oligocene epoch} includes quartz-calcite-adulaire epithermal veins (Ag-Au) of geothermal-volcanic filliation. At Guanajuato mining District; ore minerals are: Au, electrum, acanthite, aguilarite, naumannite, polybasite, proustite, fischesserite (?); chalcopyrite, sphalerite and galena. Ore grade at Las Torres mine are: Ag 300 g/t, Au 2 g/t. At El Cubo mine because of the presence of rhyolitic domes gold grade reaches 100 g/t. Since Early Cretaceous Epoch, metallogenic concepts of heritage and permanence are valid in SG ore deposits.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3665 Mineral occurrences and deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting