Magmatic Mineralization And Prospecting Of The Huaniushan Lead-Zinc-Silver Polymetallic Ore Field In Gansu Province, China

The Huaniushan lead-zinc-silver polymetallic ore field is located in the southern part of the Beishan metallogenic belt.Frequent magmatic activity and intrusive rocks are widely distributed in this area.The latest period magmatic activity-Huaniushan intrusion has a close relation with mineralization.The zircon LA-ICPMS U-Pb dating constrains that the Huaniushan intrusion is an Indosinian composite granitoid.The first intrusive granite is the main body which formed at ca.237Ma and the second intrusive granite is small which formed at ca.227Ma.The rock assemblage includes alkali granite,syeogranite,monzonite and granite porphyry.These rocks belong to highly fractionated I-A type granites and exhibit high potassium,alkaline and quasi-aluminum to peraluminous features.The Huaniushan granitoid was divided into three units:Dongdaquan,Huaxishan and Changshui from east to west.Here we report that the three units have similar isotopic compositions.They have relatively high I_sr values?0.7072⁰.7086?and weak negative?Nd?t?values?-1.5^-2.1?,with young Nd model ages of 0.91¹.04 Ga.They also show markedly positive zircon?Hf?t?values?+3.2⁺11.8?and crustal model ages of0.58–1.06 Ga.Our results show that Huaniushan granitoid is approximately solidified at 778.9⁸26.7?and 51.1⁸5.3 MPa with the depth of emplacement varies in the range of 2.5².6 km by the methods of Al-in-hornblende.The Huaniushan granitoid formed under a tectonic setting transition from compressional to extensional from Late Permian to Early Triassic.At the intracontinental orogenic stage,mantle-derived magma grew vertically,which results in partial melting of late Mesoproterozoic to the Neoproterozoic crust.The calcium alkaline magma crystallized at high temperature and low pressure.According to the biotite thermometer,magma lower limit varies in the range of600⁶20??The molybdenum ore body is close to the center of intrusion,and the lead-zinc-silver ore body and the gold ore body are far away from the center,which constitutes a magmatic hydrothermal mineralization system as a whole.Pb isotope suggests that magma is the main source of heat and material source of mineralization,and the mineralization material comes from the deep source region.The S isotope bimodal distribution implies that the diversity of its source is controlled by surrounding rocks.The D-O isotope shows a large amount of atmospheric precipitation in mineralization,indicating that fluid mixing is an important mechanism of material precipitation.Ag mainly exists in two forms:independent mineral(AgSbS₃,Cu₃Ag₄Sb₂S₁₃)and invisible silver mineral.Based on the above research,the metallogenic model and the"trinity"prospecting model were established.The ore-forming intrusion was determined and the detailed metallogenic structural plane also studied.Taking into account remote sensing interpretation,large-scale geochemical and geophysics achievements,we identify the anomalous characteristics of ore-prospecting and the exploration direction is also proposed.