Geological Characteristics And Prospecting Direction Of Sanchahe Iron-gold Deposit In Laiwu City,Shandong Province

This paper is based on the detailed investigation project of Sanchahe Iron and Gold Deposit of Shandong First Institute of Geological and Mineral Exploration.Through field observation of Sanchahe Gold Deposit and microscopic observation and analysis of typical core and ore samples,combined with regional metallogenic geological background,geophysical and geochemical elements,the geological characteristics of the deposit,the source of metallogenic materials and the formation age of the deposit are discussed.Strata,geophysical and geochemical prospecting indicators have been determined.The strata directly related to the formation of the Sanchahe deposit are the limestone of the Wuyangshan Formation of the Ordovician Majiagou Group and the ore-controlling structure is the Zhangbaqiu fault.As a result of magma intrusion,a large number of limestone was swallowed,faulted and inverted,forming a trap contact zone structure.Strong chemical reactions occur between the intrusive body and surrounding rock near the captured body.The components of Si,Al,Ca and Mg are exchanged in the reactions,and skarn deposits are formed.The ore types are mainly magnetized skarn type gold ore and pyritized magnetized skarn type gold ore.The main ore structure is scaly granular metamorphic structure,while the secondary ore structure is scaly fibrous metamorphic structure and columnar fibrous metamorphic structure.Surrounding rock alterations include skarnization,epidemic,chloritization,magnetization,pyritization,chalcopyrite mineralization and gold mineralization.The mineralization of the deposit can be divided into three metallogenic stages:early skarn stage,late skarn stage and sulfide stage.The sulfur isotope analysis shows that the sulfur of mantle-derived magma is the main contributor,accounting for 82%-95%,while marine sulfate accounts for only5%-18%.The ²⁰⁶Pb/²⁰⁴Pb value of Tietonggou intrusion is 17.66-18.53;²⁰⁷Pb/²⁰⁴Pb value is 15.41-15.53;²⁰⁸Pb/²⁰⁴Pb value is 35.71-41.46.In the lead isotope tectonic environment evolution diagram,most sulfide samples are located outside the upper crustal evolution curve,indicating that the ore lead is mainly derived from crustal materials.The biotite test in skarn of similar typical regional deposits shows that magnetite skarn is mainly formed between 128 Ma and 133 Ma,and gold in Sanchahe gold deposit is mainly formed in sulfide stage.The main metallogenic time of Sanchahe gold deposit can be calculated by cooling rate from 128 Ma to 121 Ma.The magnetic anomalies in this area are mainly caused by magnetite and magnetite skarn.Magnetized granite,skarn and hornblende have certain magnetism,while marble,limestone,sandstone and granite have weak magnetism.The magnetic anomaly delineated is not closed at the southern end.Throughout the whole region,the magnetic anomaly polarization map shows that the magnetic anomaly belt is approximately NNE-trending,the 500 nT magnetic anomaly isoline is approximately elliptical in a long axis direction of about 600 m,and the width of the short axis direction is about 180 m.The metallogenic geological conditions of Sanchahe area are analyzed,and the prospecting criteria of skarn type gold deposits in this area are determined.The analysis shows that within the scope of Sanchahe mining area,there are prospecting prospects near the fault in the north and south side of the deposit and in the deep part of the existing orebody.On the regional scale,the carbonate contact zones near Laiwu mine,Jiaoyu mine and Jinniushan mine have good prospecting potential.