Abstract

The Cantera mine is one of the few operating mines of the formerly great silver camp of Zacatecas, Mexico. The mine consists of a series of sulphide orebodies along the Cantera Fault, about 5 km east of the city of Zacatecas. The Cantera Fault is a large normal fault striking N70 degrees -80 degrees W and with an average dip of 50 degrees SW. North of the fault, a series of indurated Mesozoic (?) shales or clay slates has been intruded by a small gabbroic stock with associated dikes and sills. South of the fault, the Zacatecas Valley is underlain by a thick sequence of Miocene (?) agglomerates, tuffs, and rhyolites. The volcanism culminated with the eruption of at least 100 meters of rhyolite, presumably blanketing the entire Zacatecas Valley. At La Cantera, this cover has been removed by erosion.The orebody at La Cantera is an epithermal breccia filling deposit in which there has been considerable replacement. Although mining operations have obscured the vein structure, old reports indicate that the vein consists of two parts--a silver-rich quartz hangingwall vein, and a sulphide footwall vein. A suggested paragenetic sequence for the primary minerals is: quartz, sphalerite-chalcopyrite, galena, pyrite, quartz, pyrite, calcite. Silver sulphides are presumably present, but their position in the paragenetic sequence is uncertain.The amount of eluvial silver ore spread over the south slope of the Cerro de la Cantera indicates that 400 meters of vein material have been removed by erosion. The age of the mineralization is not definitely known, but is probably post-Miocene.The orebody has been broken by later north-south cross-faults with associated quartz veins. Contrary to previous opinion, at La Cantera these cross-faults exercise no control over the distribution of the ore shoots within the Cantera Vein.

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