Geochemical characteristics and geochronology of porphyroid biotite monzogranite from the Reshui Mo polymetallic deposit, East Kunlun Mountains

The Reshui Mo polymetallic deposit is located at the North Kunlun magmatic arc, where lots of intrusive rocks occur. Geochemical data reveal that the porphyroid biotite monzogranite from East Kunlun is rich in silicon (67.64%-71.09%), Al₂O₃ (13.8%-14.57%), Na₂O(2.23%-3.02%), and K₂O(3.95%-5.18%), with ratios of K₂O/Na₂O being 1.35-2.32 and A/CNK being 0.86-1.11, 1.01 on average, suggesting that the granite should belong to high potassic calc-alkaline and I type granite. The porphyroid biotite monzogranite is intensively depleted in HFSE (Ta, Nb, mCe), enriched in LILE (Rb, Th, U, K, Pb), and poor in P, Ti. The total rare earth elements (ΣREE) are 94.27×10^-6-127.44×10^-6, with an average of 110.92×10^-6. The rare earth element distribution curve shows the right-inclined type, and has characteristics of obvious enrichment of light rare earth and depletion of heavy rare earth elements. LA-ICP-MS zircon U-Pb dating shows that the formation age of the rock is (230.9±1.4) Ma, belonging to Indosinian stage. The molybdenum polymetallic deposit is closely related to the magmatic activity during this period. Based on tectonic history and the structure environment in combination with the geochemical characteristics, the authors hold that the porphyritic biotite monzonitic granite of the Reshui deposit was formed at the structural transformation stage, and Rershui area has potential for finding porphyry deposits.