Geology and geochemistry of the Early Carboniferous Eastern Sawur caldera complex and associated gold epithermal mineralization, Sawur Mountains, Xinjiang, China

Volcanic rocks associated with Early Carboniferous gold mineralization are well exposed in the eastern part of Sawur Mountains, Xinjiang, China. New results for these volcanic rocks recognize the Eastern Sawur caldera complex and broadly subdivide the volcanic-magmatic activity into the three cycles and nine lithofacies. The Eastern Sawur caldera complex consists of at least one elliptical andesite caldera, associated with later and smaller circular andesite caldera, mafic volcanic necks and mafic to felsic dikes. The effusive rocks have a transitional character from calc-alkaline to tholeiite, range from porphyritic basalts, basaltic andesites, andesites to dacites, are enriched in large ion lithophile elements (LILE) and depleted in high-field strength elements (HFSE) relative to NMORB, with a pronounced negative Nb anomaly. Chondrite-normalized rare earth element (REE) patterns show enrichment in the light REE relative to heavy REE. The volcanic rocks have near-uniform initial Sr-11/Sr-16 (0.70335-0.70362) and Nd-143/Nd-144 (0.51254-0.51259; epsilon(Nd) = 3.5-4.7) ratios. These rocks originated from the partial melting of a subduction-modified mantle Wedge in a subduction setting. The wedge represents an enriched MORB mantle source with some transfer of subduction components to the wedge during the magmas formation. Crustal assimilation could have played a role in petrogenesis during the ascent of the magmas. Geochemical characteristics of these volcanic rocks are consistent with their formation in a subduction-related tectonic setting during the Early Carboniferous. A close spatial and temporal relationship exists between the volcanic rocks and hydrothermal gold mineralization in the Sawur Mountains. Intermediate to silicic volcanic rocks and/or caldera fracture system host a number of gold deposits. There is evidence for a direct genetic association, i.e. the two processes are linked by the common mantle-derived sources. Previous studies have suggested that ore-forming fluids mainly derived from mantle. This study indicates that a direct link exists between the formation of mantle magmas in subduction zones and the generation of epithermal gold deposits. (c) 2007 Elsevier Ltd. All rights reserved.