Hydrothermal alteration of volcanic rocks hosting the Late Jurassic-Early Cretaceous San Nicolás VMS deposit, southern Zacatecas, Mexico
| Autor: | Luis F. Vassallo, José Jorge Aranda-Gómez, José Gregorio Solorio-Munguía |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | Universidad Nacional Autónoma de México UNAM Redalyc-UNAM Revista Mexicana de Ciencias Geológicas (México) Num.2 Vol.32 |
| Popis: | "San Nicolás is a Late Jurassic-Early Cretaceous, stratiform Zn-Cu-Ag-Au volcanogenic massive sulfide (VMS) deposit located incentral Mexico, with a total resource of 99 Mt of ore grading 1.36 % Cu,1.64 % Zn, 0.41 g/t Au and 24 g/t Ag. At San Nicolás mining districtthe ore deposits are related with submarine graben-horst structuresproduced by the opening of the Gulf of México. San Nicolás VMSdeposit is at the right side of a graben structure, fed through a normalgrowing fault called "La Panza". The host-rock succession consists ofa variably altered rhyolite lava dome in the hanging wall and a basaltdacite-dominated volcano-sedimentary sequence in the footwall. Thesulfide deposit and hosting volcanic sequence were metamorphosedunder lower greenschist facies.A laterally continuous footwall alteration zone extends beneaththe entire district (~80 km2) and to a stratigraphic level at least200 m below the several ore lenses. The bulk of this zone is occupiedby feldspar-destructive, muscovite-biotite-chlorite-rich, mottledalteration facies with disseminated pyrite. The ore mineralizationwas controlled by a fault zone with intense quartz-pyrite alterationand represents the principal fluid pathway during mineralizinghydrothermal activity. Locally, quartz-K feldspar alteration facies occuron the edges of the system, whereas calcareous alteration and chloritepyritealteration facies occur in the upper part of footwall volcanics,next to sulfide lenses. Porphyritic basalts, plus basaltic pillow lavasand volcanic breccias in the hanging wall are unaltered or weaklyaltered.Carbonate alteration (formation of dolomite and/or ankerite)probably represents the initial phase of hydrothermal activity. Thiswas followed by diffuse upwelling of acidic hydrothermal fluidscausing dissolution of underlying limestones and destruction ofprimary feldspars, precipitation of pyrite, and formation ofsericite, chlorite, and clay minerals. Subsequently, intense quartzpyritealteration was directly associated with mineralization.The San Nicolás footwall alteration zone shows systematicgeochemical changes with increasing proximity to the ore bodies. Theseinclude Na depletion and elevated Mg, S, AI (AI=100*[MgO+K2O]/[MgO+K2O+Na2O+CaO]), CCPI(CCPI=100*[MgO+FeO]/[MgO+FeO+Na2O+K2O]),as well as Mo, Bi, and As. These geochemicalfeatures can be used in exploration for massive sulfide deposits asguides to ore, at the district scale, and in discrimination of prospectivehydrothermal from unprospective diagenetic alteration systems at theregional scale." |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|