Geological Characteristics And Metallogenic Regularities Of Northern Sanjiang Porphyries Mo(-Cu) Ore Belt,Southern Qinghai

Recent studies on the Northern Sangjiang ore belt ,Southern Qinghai,reveal that the ore belt have excellent metallogenic conditions and geological background to form the Large, extra large metal deposits and expect to have breakthrough in prospecting after intensive work.By detailed field geological work and systemic modern analysis work ,this dessertation studies the geological Characteristics ,petrology,geochemistry and geochronology of the ore-bearing porphyries,such as Narigong and Lurige deposits.to research the dynamical backgroud,mineralization features and deposit model in Northern Sangjing ore belt and compare orther porphyies deposits in Sangjiang belt.The main conclusions were drawn as follows:The Northern Sangjiang ore belt's ore-bearing porphyries include Biotite monzogranite porphyry and Light-colored quartz monzonite porphyry.Ore stone show Veinlets- disseminated structure and mesh-vein texture.Mineralization is mainly Mo-Cu,and associted Bi,Te.This paper carries out the porphyry zircon LA ICP-MS U-Pb isotope dating method and Molybdenite Re-Os isotope dating method, the first time for Lurige and detailed measurements for Narigongma .The rock-forming ages of Lurige range from 61.7Ma to 62.1Ma, and Narigongma deposit range from 42.9Ma to 43.4Ma.The Molybdeum mineralization age at Lugrge is 60.7±1.5Ma,and Narigongma is 40.5±0.8Ma.So Narigongma and Lurige porphyry deposits are two separate magmatic-hydrothermal ore forming process,and the span age of mineralization age and rock-forming age is about 2-3Ma. Therefore,since Cenozoic the Sanjiang porphyry deposits have two large-scale presence of magmatic mineralization events.The element geochemical features in Northern SanJiang belt show adakite magmatic affinity ,similar to Yulong ore belt.The ore porphyries rocks are high SiO₂,k₂O and high k₂O/Na₂O ratio and mainly high-K calc-alkaline porphyry-shoshonitic series.The rocks are all enriched in large-ion lithophile elements(eg.K,Rb,Sr,Ba,Th,La)and light rare earthelements,depleted in high field-strength elements and heavy rare earth elements.The ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb,²⁰⁸Pb/²⁰⁴Pb values of Northern Sanjiang ore-bearing porphyries range from 18.4100～19.4290,15.6090～15.6850,38.5770～39.5228.The (⁸⁷Sr/⁸⁶Sr)_t,(¹⁴³Nd/¹⁴⁴Nd)_t values range from 0.702873～0.705859, 0.512573～0.513204, and the values ofεNd(t)is 0.30～0.64 Roughly.The Sr-Nd-Pb isotope of Northern Sanjiang ore belt,Southern Qinghai,were very close to Emll,so the intrusive rocks maybe come from the account of enriched mantle.Theδ³⁴S value of Narigongma'sulfide was 4.0‰⁷.1‰and Lurige was -2.60‰⁵.8‰.Narigongmaδ¹⁸O values of the Forming fluid which Ore-forming fluids and quartz Reach equilibrium was 0.6‰～3.0‰,and Lurige was -0.76‰～3.54‰.As the depth increased,δ¹⁸O become larger andδD become smaller.Theδ¹³C values of the dolomite are smilier with magma/mantle source.So the Ore-forming metals of Northern Sanjiang belt comes from magma and the ore-forming fluid comes from magmatic hydrothermal fluids.Based on the comprehensive study,the thesis propose porphyries mineralization model and prospecting indications and summarize the metallogenic regularity .The two large-scale regional porphyries mineralization was coused by the conversion of Strike-slip fault tectonic stress in Northern Sanjiang belt ,Southern Qinghai.