173 / 2015-09-15 09:47:23

Race elements and Sr-Nd isotopes of scheelite: Implications for the W-Cu-Mo polymetallic mineralization of the Dahutang deposit, South China

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We report elemental and Sr-Nd isotopic data for scheelites from the newly discovered Dahutang W-Cu-Mo polymetallic deposit (South China), one of the largest tungsten deposits in the world with an estimated WO3 of 2 million tones, in order to determine its source region and implications for genesis of the deposit. Scheelite is the most important ore mineral in the Dahutang deposit; its rare earth elements (REEs) and Nd-Sr isotopic compositions can be used to constrain the origin of the mineralizing fluids/metals. Our data reveal that the REEs of scheelite are controlled by the substitution mechanism 3Ca2+=2REE3++□Ca, where □Ca is a Ca-site vacancy. The scheelites from the Dahutang deposit can be grouped into two types based on the distinct Eu anomalies: type 1 with negative Eu anomalies and type 2 with positive Eu anomalies. The variation of Eu anomalies recorded the ore-forming processes. The negative Eu anomalies were inherited from the porphyritic granite and the positive ones from destruction of plagioclase of country rock during fluid-rock interaction. The variations of the cathodoluminescence (CL) colour of a single scheelite from red to blue and to yellow are linked to the increase of REE contents. The high Nb, Ta, LREE contents and LREE-enriched REE patterns of scheelites from the Dahutang deposit reveal a close relationship with magmatic hydrothermal fluids.

The scheelites from the Dahutang deposit are characterized by low εNd(t) values (-6 ～ -8) and usually high initial 87Sr/86Sr ratios (0.7230 ～ 0.7657), different from those of scheelite from the vein-type Au-(W) and W-(Sb-Au) deposits. The εNd(t) values of scheelites are consistent with those of the Mesozoic porphyritic granite. However, the high and significantly varied initial 87Sr/86Sr ratios of the Dahutang scheelites indicate that Neoproterozoic Shuangqiaoshan Group schists/gneisses may have contributed to the ore-forming fluids/metals.