What controls Sn-W mineralization in granite batholith: A case study from the world-class Dulong Sn-Zn polymetallic ore deposit of SW China

Abstract

Magmatic-hydrothermal ore deposits hosted in granitic batholiths are an important source of tungsten (W) and tin (Sn). However, it remains enigmatic whether and how the Sn-W mineralization is triggered by the spatially associated batholith because the Sn-W-bearing granitic rocks are more likely to occur as small intrusions. Here we used a combination of LA-ICP-MS cassiterite U-Pb dates, published whole-rock geochemical, and high-precision exploration data to evaluate a genetic link between the world-class Dulong Sn-Zn polymetallic ore deposit and its spatially associated batholith in SW China. Our new cassiterite U-Pb dates indicate that the Sn-Zn and Sn-Cu mineralization events were temporally associated with the emplacement of concealed granites and porphyritic dykes respectively, consistent with the spatial pattern between Sn-Zn-Cu mineralized zones and granitic rocks in the Dulong ore district as revealed by the high-precision exploration data. The compiled data presented in this study show that these granitic rocks throughout the batholith are of S-type and highly fractionated affinities, and their parent magmas might experience similar degrees of fractionation. Importantly, the low Nb/Ta ratios (most < ∼5) in granites of the Dulong ore district are markedly differentiated from highly variable values (∼2.0 to ∼ 9.4) in the batholith, which may be caused by the extensive sub-solidus interaction with late magmatic fluids. Furthermore, the granites of the Dulong ore district are significantly poorer in Sn-Zn contents than those of the Laojunshan batholith, suggesting the extensive Sn-Zn-rich fluids exsolved from highly evolved granitic magmas could lead to a significant decrease in Sn-Zn contents in consolidated granites and the formation of Sn-Zn ore deposit, due to the relatively high fluid/melt partition coefficients of Sn and Zn. In conjunction with evidence from previous numerical and mineralogical models, and the spatial pattern between Sn-Zn mineralized zones and apical parts of concealed pluton in the Dulong ore district as revealed by high-precision drill data, we propose a model involving highly evolved granitic magmas that formed batholith, apical portions of which as the emanative centers of Sn-Zn-rich fluids played a crucial role in the formation of the world-class ore deposit.