Genesis Of The Narigongma Porphyry Molybdenum(-Copper) Deposit In Qinghai

Narigongma porphyry molybdenum(copper) deposit is located in Southern Qinghai. And it is also in the Northern part of Yulong metallogenic belt. It seems to have a great metallogenic capacity. After a exhaustive research of Narigongma porphyry deposit, also with Hf isotope composition analysis, we understand the evolution of the magma, also with the alteration types and mineralization types of this deposit. Also, the alteration zoning model is established. And, the geological record of the vein is well studied.After we gave a deep research with the veins(A veins, B veins, and D veins), together with associated alterations:K-silicate alteration (biotite-K feldspar), propylitic alteration (chlorite-epidote±calcite), and feldspar-destructive alteration (sericite±kaoline±calcite). We find that K-silicate alteration and propylitic alteration was overprinted by feldspar-destructive alteration. Then the model of the alteration zoning is built. Molybdenum mineralization is always accompanied by feldspar-destructive alteration, especially the phyllic alteration, and quartz-molybdenite±pyrite±chalcopyrite vein is always contribute the most of the amount of metal.Hf isotopic analysis gives us evidence that the porphyries in Narigongma have positive εHf(t):the value of light-colored fine-grained granite porphyry is from+1.35to+8.68, and the value of quartz diorite is from+4.14to+7.35. In that case, we know the both of the two types of porphyries are of the characteristic of depleted mantle.Fluid inclusions are also studied. The homogenization temperature of A vein fluid inclusions is between326.4～409.1℃(most between270℃～350℃, high temperature temperature), and that of B vein is between253.2～485.6℃(most between270癈～350癈, medium temperature). The fluid inclusions of A vein is in medium-high salinity (9.0wt%～51.6wt%) and also B vein(7.7wt%～22.2wt%).