Multivariate statistical analysis and scheelite ore formation in the Longjiaoshan-Fujiashan W-Cu skarn deposit, Middle-Lower Yangtze River metallogenic Belt (Eastern China)

Abstract

The Longjiaoshan-Fujiashan W-Cu skarn deposit is located in the Edong ore district of the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), Eastern China. To elucidate the W ore formation, we analyze the scheelite ore samples with SEM-CL imaging, mineral geochemical analysis, and partial least squares-discriminant analysis (PLS-DA). Detailed field and microscopic observations show that the scheelite comprises four generations (schA, schB1, schB2, schC) formed in three stages (I to III). EPMA mapping, combined with SEM-CL, reveals that schC (high W generation) is observed mostly in stage I to II. To identify the discriminant elements separating the different sample classes (different ore stages, scheelite generations and scheelite F content) based on scheelite compositions, we carried out partial least squares discriminant analysis (PLS-DA). Binary scatter plots suggest that Mo is a good discriminator in all discriminant groups. Cesium and As are good discriminators for the scheelite ore stage groups, As and Sr for the scheelite generation groups and Nb and Ta for the scheelite fluorine content groups. These discriminators could guide skarn-type W (scheelite) ore prospecting. The close relation of Nb-Ta with high-fluorine scheelite and highly-fractioned granite suggests that highly-fractioned granites and F-rich fluids have contributed to scheelite formation. We propose a multistage scheelite ore-forming process at Longjiaoshan-Fujiashan.