Characteristics And Metallogenic Prospect Of The Jinbaoshan Mafic-Ultramafic Complex, Yunnan Province

The Jinbaoshan Pt-Pd deposit in Midu county of Yunnan province which is the largest independent Pt-Pd deposit in China which belongs to the magmatic Cu-Ni sulfide deposits and it’s exist in the Jinbaoshan mafic-ultramafic complex, therefore, it’s important to research the mafic-ultramafic complex deeply. The Jinbaoshan mafic-ultramafic complex is located in the west side of Yangtze plate and the west side is about 5 kilometres to Ailaoshan structural belt. On the basis of field geological investigation, the further studying of the complex rock mass characteristics of rock mass and made some progress by the microscopic identification, electronic probe and geochemical analysis, SHRIMP zircon U- Pb dating method, etc.The Jinbaoshan complex serpentinized strongly, the type of rock include mafic rock and ultramafic rock, which the mafic rock include gabbro and dolerite and the ultramafic rock mainly is bronzite peridotite. Because of the PGE minerals exist in the ultramafic rock instead of mafic rock, the article foucus more on the ultramafic rock of the complex. Jin Baoshan ultramafic rock mineral composition is olivine and orthopyroxene which mainly is peridot(the content of forsterite is from 84% to 86%) and bronzite(the content of enstatite is from 83% to 89%)and followed by monoclinic pyroxene, calcium magnesium olivine and chromite, hornblende and biotite minerals.Because of the rock alteration is strongly, the antigorite and chrysotile develop in the complex.Chemical analysis of major element for the ultramafic complex shows that the content of SiO2 is from 32.5% to 40.52%, MgO from 29.95% to 36.32%, TFeO from 7.31% to 20.19%, Al2O3 from 1.41% to 5.90%, TiO2 from 0.36% to 1.53%, P2O5 from 0.03% to 0.17%,CaO from 0.14% to 5.05%, K2 O from 0.05% to 0.22%, Na2 Ois from 0.01% to 0.51%, MnO from 0.09% to 0.2%, m/f from 3.06 to 5.98, characteristic of iron-ultramafic rock and the original magma belongs to continental tholeiite series. The solidification index is from 56.87% to 82.81% and mafic index is from 16.79% to 43.00%,and the ore is more higher solidification index than the rock.Chemical analysis of rare earth elements of the ultramafic complex shows that the REE content is higher which the LREE content is from 15.36×10-6 to 37.77×10-6 and the HREE content is from 2.32×10-6 to 4.86×10-6, Σw(Ce)/Σw(Y) is from 4.35 to 7.97.The REE distribution pattern shows a flat right decline, representing evident enrichment in LREE and strong fractionation in the late magmatism. The rock is of ngative Eu anomaly with an average δEu value of 0.74. The rido of δEu is from 0.43 to 1.11. [w(La)/w(Sm)]N is from 1.70 to 3.32,representing the original magma is from the enrich metasomatic mantle.Chemical analysis of rare earth elements of the ultramafic complex shows that the strong incompatible trace elements are more richer than wake incompatible trace elements. Some elements include K,Ba,P,YandYb is lossing evidently and Sr is losing strongly and which owes to the plagioclase crystal fractionation. Nb/La is from 0.47 to 1.21, Nb/Ce is from 0.21 to 0.51, Lu/Yb is from 0.10 to 0.18, Zr/Hf is from 24.00 to 39.78, Nb/Ta is from 5.99 to 29.08, which compared with the primitive mantle and MORB is big difference, representing the magma suffer from a strong hybridization of crust materials.The diagenesis ages of the Jinbaoshan complex is 260 Ma. In the process of the original magma invasion,it suffers from a strong hybridization of crust materials which promoted the sulfide to develop liquation. The PGE sulfide minerals exist in the ore of sideronitic structure and disseminated structure which formed in the original magma liquation. Therefore, the original magma liquation is important to lead the PGE sulfide minerals to enrich.The Jinbaoshan ultramafic rock mainly is bronzite peridotite, and the content of forsterite and enstatite is close enough, so the ore-bearing potential of the Jinbaoshan ultramafic rock is very well.The PGE elements of the Jinbaoshan deposit in the form of the sulfide exsit in the ultramafic complex, and the content of MgO shows that it belongs to high temperature sulfide-barren series and the content of sulfide is scarce.So the PGE of ultramafic complex is low grade.The Deju mid-mafic volcanic rocks belt locates between the Jinbaoshan complex and the Ailaoshan structural belt, and it’s basalt belongs to continental tholeiite series which geochemical characteristics are same with the Jinbaoshan ultramafic complex.During the late Permian period, the westward subduction of Ailaoshan oceanic crust led to the formation of continental aulacogen in the west margin of Yangtze terrene and to the formation of mafic-ultramafic igneous rocks in the Deju aulacogen which closely related to the Jinbaoshan ultramafic rock in genesis. The article considers that the magmatic vent maybe in the Deju aulacogen.Therefore, attention should be paid to the geological and geochemical studies on the Deju mid-mafic volcanic aulacogen so as to expand the exploration prospect.