Geochemical Characteristics Of The Yajia Polymetallic Deposit In Northwestern

The Beiya multi-metal deposit, an important part of the alkali porphyry belt of the Jinsha River-the Red River, is located in the western margin of the Yangtze block. This multi-metal mine is a super large deposit whose gold reserves has reached the size of the super-large ore.It also has some other accompany metal minerals such as iron, copper, silver, lead, zinc and so on. According to the basis of previous studies, we analyzed and researched the gold characteristics of mineralization, the diagenetic and ore forming material source of this deposit by researching the geological background, gological characteristics of the deposit, rock geochemical characteristics, fuid inclusions and other aspects. The main results are as follows:Through field investigation and combined with previous data.The form reason of the Beiya mine who contains gold and polymetallic can be divivded into two system and four types:Porphyry-skarn mineralization system, including skarn Au-Fe-Cu mine, porphyry Au-Fe(Cu) mine and the hydrothermal vein Pb-Au-Fe-Ag-(Cu) mine; The supergene metallogenic series are main weathering-accumulated type Fe-Au mine. We can divide the formation of Beiya mine into two-stage and four parts:The first stage is endogenic minerogenetic phase that includes skarn stage, the stage of retrograde alteration, quartz sulfide phase, carbonate phase and while the second stage is the supergene oxidation time.Through the ananlysis of these elemnts that belong to,the intrusive rock body, such as major elements, trace elements, REE and platinum group, we concluded that the monzonite porphyry is the most widespread magmatic rocks in BeiYa areas. And related with mineralization very closely at the same time. Some of the exposed monzonite porphyry had happened potassium leads to higher K2O, Rb and Pb content, and the lower CaO, Na2O and Sr content. Overal, monzonite porphyry, Potassium monzonite porphyry, and biotite monzonite porphyry having the same geochemical composition. Because they share the same provenance.The BeiYa potassic porphyry has relative higher contents of SiO2(SiO> 67 wt.%) and Al2O3 (13.45-15.22wt.%). It also enriched in Sr (365 ×10-6-930×10-6)and LREE while lacks of HREE. Its ratios such as Sr/Y and (La/Yb) N are relatively higher and have no significant negative anomaly of Eu, showed geochemical characteristics adakites, but it is sign that high (Na2O+K2O), high (K2O)/Na2O ratio and low MgO, Cr, Ni which is different from typical adakites.The BeiYa lamprophyre have the features that alkali-rich, high potassium, enrichment of K, Rb, Ba and the like. Large ion Pro stone elements and light rare earth elements, loss of heavy rare earth and Nb, Ta, Zr, Hf high field strength elements.It is indicated that the alkali porphyry of BeiYa mine may originate from the fusion of the earth’s crust under the garnet amphibolite faciesrock source. Platinum family elements’ analysis shows that gold ore samples’s distribution patterns of PGE and PGE lamprophyre distribution patterns are the same. So Beiya gold mine’s form reason and the sources may have some relationship with the Himalayan lamprophyre dikes. Talk about main parameters of PGE gold ore sample, such as Pt/Ir, Pd/Ir and Pt/Pd are almost the same, and the differences between lamprophyre and quartz syenite porphyry is very small:Pt/Pt* is less than 1,0.49 to 0.81 which the average number is 0.672. The number beetween Huang quartz porphyry and syenite porphyry Pt/Pt*. The data shows that the source of gold and minerals from those two types of intrusive rock are related to each other.The study of fluid inclusion about the gas-rich fluid inclusions in the skarn minerals manifests that the riched water vapor fluid is differentiated after the intrusion of magma rocks. The first step is isolated from water which is vapor-rich fluid, and contact with the rock skarn and magnetite mineralization zone which is formed; The second step is that as the magma crystallization performed, CO2 have divide from a large number of ore-forming fluids. Formation of CO2-rich fluids. At last. The CO2-rich fluids Formed and at the time of late crystalline, the formation of Copper and molybdenum mineralization in its Porphyry body; In the process of forming fluids in diffusion from the periphery to the rock formations Because siderite, dolomite and other carbonate minerals’s form may consumed CO2, Simultaneously. With the heat of ore-forming fluid loss and metasomatic reaction of the surrounding rock, the Ore-forming fluid temperature had decreased. It will be form in the advantageous construction site which forms like horizon hydrothermal type with Gold lead and zinc mineralization.