Polymetallic epithermal fissure vein mineralization, Topia, Durango, Mexico; Part I, District geology, geochronology, hydrothermal alteration, and vein mineralogy

摘要: The Topia district lies on the western flank of Sierra Madre Occidental structural arch and Tertiary volcanic plateau. Beneath unmineralized mid-Tertiary silicic ignimbrites a kilometer-thick sequence early andesitic lavas pyroclastics resting Mesozoic limestones marine clastic sedimentary rocks. Laramide geanticlinal uplift along produced regional tilting major fracturing pile. Following an interval erosion, was intruded by granodiorite stocks, northeast-trending set faults mineralized as Ag-Zn-Pb-Au-Cu-rich fissure veins. Mineralization followed tectonic quiescence then eruption more than kilometer Oligocene ignimbrites. K-Ar dating igneous rocks mineralization yields age 46.1 m.y. for one date 43.8 vein adularia, 43.5 hydrothermal celadonite, 44.0 andesite lava which reset thermal event. A 37.9 lowermost rhyolite welded tuff corresponds to initiation widespread ignimbrite eruptions in Sierra. Fissure-filling accompanied development alteration comprising (1) narrow (<1 m) quartz-sericite-pyrite envelope (___ adularia ___ chamosite _ kaolinite hematite celadonite) that grades outward into (2) variably silicified oxidative zone occupies entire between veins at elevations above oTe horizon. distal facies envelopes consist inner intense celadonite + quartz calcite illite clinochlore subfacies outer veinlets nearly fresh rock. At below ore horizon, local is absent silicification passes conventional propylitic envelopes. Chemical gains losses porosity changes have been monitored quantitatively across succession Oblique .tensional slip having gentle convex concave irregularities steps surface alternating dilatant (fissure) convergent (shear zone) intervals each fault. Open were filled or less symmetric, crustified precipitation walls, whereas wall-rock-replacement characterizes shear intervals. In vein, restricted vertical 100 200 m (the "ore horizon"), downward barren coarsegrained quartz-rich filling upward barren, cherty quartz-calcite-barite-rich filling. horizon commonly contains subequal amounts sphalerite, pyrite, galena, quartz, with minor arsenopyrite, marcasite, chalcopyrite, Ag-rich sulfosalts, electrum, chamosite, muscovite, carbonates. Locally, massive sphalerite millimeter- centimeterthick crustification bands dominates paragenetic sequence. Crustification dominated calcite, barite are predominantly fine grained; they precipitated from lowsalinity, boiling fluids. Intercalated sulfides characteristically very coarse grained (to 10 cm) high-salinity fluid inclusions (7-23 wt %); no primary vapor-dominant recognized pyrargyrite. Precipitation coarse-grained punctuated recurrent effervescence fluids within electrum