Stuty Of Metallogenic Forecast With Large Scale In Zinjinshan Copper-gold Ore Concentrated Area

The study area, Zijinshan ore concentrated area of Shanghang county, Fujian province, is located at the overlapped zone of NE trending Songxi-Shanghang volcanics belt and NW trending Shanghang-Yunxiao tectonomagmatic activities belt with focus on Zijinshan gold-copper deposits and has an area about 3500km2. The characteristics , formation, development and evolvement of main structures and ore deposits are completely summarized in the study area and the relationships of teconomagmatic activities and metallogeny (were)are explained detaily. Furthermore, the controlled factors of ore-forming are studied systematically , integrated with the temporal and spatial distribution, geological and geochemical features of Mesozoic granitoids and volcanics and their correlation to Au-Cu mineralization Based on the cluster analysis of ore deposits in the study area, the enrichment path of ore materials are traced by use of the hierarchical dendrogram of geochemical block to reduce the prospect target gradually in metallogenic forecasting of large scale in the ore concentrated area,. In addition, the storage of resources has increased by verifying the potential geochemical and geophysical abnormities and farther drilling . The important improvement and cognition during this work are as follows:1.New improvement was is made"tectonic structure"is put forward about the geological strusture related to the minerallization within the Zijinshan ore cluster. Tectonically, the Zijinshan ore cluster is located at the western part of Mesozoic volcanics belt which spreads along the southeastern margin of China and at the southwestern margin of Minxinan depression. It lies between NE trending Changle-Nanao crustal fault on east and Zhenghe-changding lithospheric fault on west. The secondary structures belong to inclined meeting part between NE trending Songxi-Shanghang fault and NW trending Shanghang-Yunxiao deep fault. In the ore field, the ore-controlled strutures are mainly displayed as crossing of two suits of faults with NE trending and NW trending, which make a grid frame. The response among these tectonic structures is coupling of background tectonic-controlling structure and metallogenic structure. 2."body in body"is put forward about the magmatic rocks related to metallogeny within Zijinshan ore cluster. The study area goes through multiple cycles, namely,Jialidong,Hualixi-Yinzhi,Yanshan and Himalaya four structural cycles and then the structure in the study area is complex and is characterized by multiple overlaping. Within the ore cluster, the intrusions related to minerallization are multiple and the ore body occurs in the granule granite of Zijinshan composite batholith, which forms the manner of"body in body". Temporally, the Mesozoic magmatic rocks are restricted in late Jurassic and early Cretaceous and the sequence of formation from morning till night is:Zijinshan complex (late Jurassic granite)→Caixi pluton (late Jurassic to early Cretaceous granite)→Shanghang-Bitian volcanic basin (early Cretaceous volcanics)→Sifang pluton (early Cretaceous granodiorite)→Zijinshan volcanic apparatus (early Cretaceous volcanics-cryptoexplosion breccias-subvolcanics -porphyry)→Ruoboling pluton (early Cretaceous granodiorite porphyry). Spatially, it is belongs to NE trending Jurassic and NW trending early Cretaceous magmatic belt. The mechanism behave as transition from extrusion to extention regionally.3."altered alteration"is brought forward about the alteration relevant to minerallization within Zijinshan ore cluster. From late Jurassic to early Cretaceous, the wall rock alteration in Zijinshan ore cluster are classified as four phases: (1) the postmagmatic hydrothermal alteration; (2) subvolcanic hydrothermal alteration including dacite porphyry hydrothermal alteration, earlier cryptoexplosive alteration, later cryptoexplosive alteration epoch, hydrothermal alteration epoch and residue hydrothermal alteration epoch; (3)porphyry hydrothermal alteration; (4) superficial alteration. The action of four stage can be thought as"alteration of alteration",and the distribution of alteration is controlled by both NW trending fault and volcanic .mechanism, which is in the model of fracture-center.The altered zone can be classified as quartz-dacite-alunite assemblage, quartz-sericite-dacite assemblage and quartz-dacite assemblage. Accrding to the relationship of the alteration and the minerallization, pre-minerallization, accompanied minerallization and post-minerallization alteration can be identified.4. Multi-floor building metallogenic mode of volcano-intruded rock was put forward in the Zijinshan ore cluster. Zijinshan large-scale Cu-Au deposit is the first high-sulphur epithermal type deposit found in China mainland. Porphyry Cu-Mo deposit, large-scale mesothemral Cu deposit, large-scale low-sulphur type epithermal Ag-Au-Cu deposit and U deposit were discovered on after the other at the deep part of Zijinshan ore district and its periphery area. These deposits , mineralized mineralization, were controlled by same geothermal system and overlapped reciprocally in space from the top down.Specifically, it is thought as"minerlized minerlization", namely,the U,Ag→Au→Au,Cu→Cu→Cu,Mo→W,Sn assembled features of different deposits display as multi-floor building.5. Middle-scale metallogenic forecast in the ore cluster is developed based on new understandings of structure, volcano-intruded rock, and ore-forming fluid. Geochemical blocks and secondary geochemical blocks were outlined by use of regional stream sedimentary geochemical mapping data. Mineralization coefficients in each grading geochemical block is calculated based on the ore reserve and the whole metal capacities of geochemical blocks. The resource potential was forecast by use of the mineralization coefficients. The prospect target reduced gradually by tracing the enrichment route of ore-forming materials and fixing on the parts which are favorable to gathering the materials of ore-forming by use of filter principle of geochemical blocks. Twenty-six targets are outlined including seven targets of A level, eight targets of B level, eleven targets of C level, which offers the geological rules for programming of geological ore-seeking.6. Based on mode study on known deposits, the ore-finding target forecast rules, ore-finding signs are put forward by use of regional comparison and synthesize evaluation of targets and study on characteristics of geology and mineral resources of zijinshan ore-field and its periphery area. , and the 15 targets , which are classified as level A, B, C by different metallogenic condition ,are selected by advantage of multiple data , namely, geological, geophysical, geochemical and remote geological characteristics in zijinshan ore-field and its periphery area. , thus, we can get the aim, large-scale ore-forming forecast, which can offer scientific rules for further ore seeking in zijinshan ore-field7. Geophysical survey and farther drilling are developed for the potential abnormities. Three-electrical-sections measurement is carried out in 330m level sap of northwestern segment in Zijinshan mining district, Longjinting copper ore district and Wenwu exploration district during this work,and the induced eletriccal data are gained and indicated the place of validated drilling hole . Drilling carried out of zijin mining group validated that the electrical abnormities are aroused by orebodies, which gets obvious effect.of ore-seeking and directs geological exploration and has the reserve increased .