GEOCHRONOLOGY AND STRONTIUM,NEODYMIUM ISOTOPE OF MANTLE-DERIVED MAGMATITES FROM THEBU′S GOLD DEPOSIT, NORTHERN XINJIANG,CHINA

Bu’s gold deposit is geographically situated in the northern side of Sawuer Mt., Western Jungar. Magmatites in Bu’s deposit including extrusive and intrusive rocks are widespread and have genetic relationship with the deposit. One volcanic suite and two intrusives are studied here. Extrusive products were formed in the Early Carboniferous with a whole-rock Rb-Sr isochron age of 347 Ma and fossil ages, while intrusions have Rb-Sr isochron ages from 310 to 329 Ma and are intrusive into the Lower Carboniferous and Upper Devonian.The isotope parameters I ranges from 0. 7037 to 0. 7046, from -5. 65^+6.67 and more,goes from +5. 65~ +7. 96, displaying that they have similar material sources and are derived from mantle magmas or their derivatives. The continental crust of Zhaisang diwa region may be initially formed in the Late-Proterozoic or even more earlier and grew probably in terms of non-proportionated model like S. China, N. American and other parts in the world.

The Character and Petrogenetic Model of the Permian Tarim Large Igneous Province

Tarim Large Igneous Province(TLIP)is the second Late Paleozoic LIPs in China after the recognition of the Emeishan LIP.The residual distribution range of TLIP is up to 250000 km2,and the largest residual thickness is 780 m.The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma.The lithological units of the TLIP include basalt,diabase,layered intrusive rock,breccia pipe mica-olivine pyroxenite,olivine pyroxenite,gabbro,ultramafic dyke,quartz syenite,quartz syenite porphyry and bimodal dyke.The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE,and mainly belong to high TiO2 series.There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin.The basalt from Keping with negative Nd and high REE value derives from enriched mantle,and the diabase and basalt from the northern Tarim Basin with positive Nd and low REE value are related to depleted mantle.The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V-Ti-magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume.The TLIP has a temporal-spatial relationship with Permian basicultrabasic igneous rock,which is distributed widely in Central Asia,and they represent a tectono-magmatic event with very important geodynamic setting.This study also systematically demonstrates the two-stage melting model for the TLIP based on our previous research work and predecessor achievements,and highlights the two types of magmatic rocks within the TLIP.The two-stage melting model suggests that the formation of the TLIP is mantle plume related.The early hot mantle plume caused the low-degree partial melting of the lithosphere mantle,while in the later stage,the plume partially melted due to adiabatic uplift and decompression.Therefore,this model carries signatures of both the"Parana"and"Deccan"models in terms of mantle plume activity.During the early stage,the mantle plume provided the heat required for partial melting of sub-continental lithosphere mantle(SCLM),similar to the"Parana Model",while later the plume acted as the main avenue for melting,as in the"Deccan Model".Basalts that erupted in the first stage have higher 87Sr/86Sr,lower 143Nd/144Nd ratios,and are enriched in large ion lithophile elements and high field strength elements,indicating a possible origin from the enriched continental lithosphere mantle,similar to the Parana type geochemical features.The basic-ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86Sr,higher 143Nd/144Nd ratios relative to the basalts,consistent with the involvement of a more depleted asthenospheric material,such as a mantle plume,similar to the Deccan type geochemical features.The first stage basalts can be further subdivided into two categories.Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes.Furthermore,this work enriches the theories describing the origin of large igneous province and mantle plume activity.

Genesis of Gold-Silver Deposits in Qingchengzi Ore Field

The gold-silver complex ore field of Qingchengzi is located in Liaohe group of Liaodong rift. The gold-silver ore bodies mainly lie in Dashiqiao group and Gaixian group. which provides ore-forming materials for the mineralization. For taking place multi-period and multi-stage magmatic activities, the ore-forming materials in the formation had had dyna- mothermal metamorphism for a long time and enriched and formed ore bodies after magmatism in Indo-Chinese and Yan- shan epoch. The ore bodies are controlled by stratigraphic formation and stored in the interformational faults and schistosity belts. Silicalite is the most important indicator for searching them. Although the Pb-Zn and the gold-silver deposits are the same series of mineralized products, their positions are different, resulting from the differences of elements nature and mineralized conditions. The gold silver deposits belong to strata-bound and hysterogeneticmesothermal-epithermal de- posit.