Major and trace element geochemistry and ⁴⁰Ar/³⁹Ar geochronology of Laramide plutonic rocks associated with gold-bearing Fe skarn deposits in Guerrero state, southern Mexico

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• 作者：Meza-Figueroa ; D. ; Valencia-Moreno ; M. ; Valencia ; V.A. ; Ochoa-Land&iacute ; n ; L. ; Pé ; rez-Segura ; E. ; et. al.
• 关键词：Fe skarn ; Gold ; Granitoids ; Guerrero ; Laramide ; Southern Mexico
• 刊名：Journal of South American Earth Sciences
• 出版年：2003
• 出版时间：August, 2003
• 年：2003
• 卷：16
• 期：4
• 页码：205-217
• 全文大小：896 K

文摘

Fe–Au skarn deposits related to intrusive centers, mostly of granodioritic composition, are widespread in southern Mexico's Guerrero state. These intrusive rocks are largely associated with the NW–SE-oriented Laramide magmatic belt that extends across most of western Mexico. The geochemical composition and ages of representative rocks from the Mezcala mining district in central Guerrero are studied to evaluate the petrogenetic aspects of the ore-related magmas. Some major and trace elements display nearly linear silica variation trends, which suggest a possible comagmatic origin. However, other elements have scattered distributions, possibly due to irregular mantle-to-crust magma mixing ratios, heterogeneities in the composition of the assimilated crustal material, or modifications during the emplacement or postemplacement processes. Major element chemistry indicates calc-alkalic metaluminous compositions, whereas trace element data suggest a volcanic arc tectonic setting, confirming that these rocks evolved from magmas generated above a subduction zone. Compared with the Laramide granites from the northern part of the belt in northwestern Mexico, which intruded a crust underlain by Proterozoic North American rocks, the studied samples are similar but relatively low in Nb and high in Sr, the middle rare earth elements (REE), P, and Zr. They also display minor Ti enrichments and a moderate depletion in the heavy REE. These characteristics may indicate a source of basaltic composition. New ⁴⁰Ar/³⁹Ar dating of granodiorites and dacite porphyries shows a north-to-south age progression from 66.2±0.8 Ma in the northern part of the belt to 62.2±0.7 Ma in the south. Moreover, the argon dates identify a younger postorogenic igneous event 35–30 Ma ago. This event is poorly documented and may have occurred after the extinction of the Laramide arc and prior to the mid-Tertiary Sierra Madre Occidental ignimbrite flare-up. On the basis of limited geochemical data, these rocks appear to be depleted in P₂O₅ and Sr and enriched in U relative to the studied Laramide granites. A Fe skarn deposit located in Buena Vista de Cuéllar, in the north central part of Guerrero, suggests that this magmatic pulse took place after the ore development of the Mezcala district.