Metallogenic Geological Conditions And Ore-prospecting In Haoquangou Area,Baiyin,Gansu Province

The Haoquangou mine area is located in the volcanic belt on southwestern side of the Baiyinchang ore field,eastern part of the Caledonian fold belt in North Qilian.This area produces the Haoquangou gold deposit,which is the largest gold deposit in eastern section of the Qilian orogenic belt.Based on the collection of previous geological,geophysical and geochemical prospecting material and research findings,and combined with geological field work and laboratory study,this paper systematically summarizes the metallogenic geological conditions of the Haoquangou mine area.Furthermore,take the Haoquangou gold deposit and Baimawa Pb-Zn mineralization for example,this paper offers a preliminary discussion about the related ore-forming fluids and their properties,material sources,metallogenic physical and chemical conditions,and the internal relations among different mineralization types.Meanwhile,the geological metallogenic body,metallogenic structure or structural plane and characteristics marks of metallogenesis of representative mineralization types are summarized in guide of the "Trinity" prospecting theory for the above research content.In this paper,the favorable mineralization information and ore-prospecting marks have been extracted by means of tectono-litho geochemistry and geophysical prospecting methods,and comprehensive information prospecting model of the Haoquangou mine area has been built.Then,combined with metallogenic geological conditions,geophysical and geochemical prospecting information,the prospecting target area was delineated.Through the above-mentioned work,the following knowledge has been obtained:1.Basic tectonic framework of the Haoquangu mining area consists of the Heishishan first anticlinorium with its secondary folds,and the NWW,NE-NEE first fault.The main exposure lithostratigraphy is Cambrian marine metamorphous acid-basic volcanic rocks consists of albitophyre,quartz-keratophyre tuff,spilite,quartz albitophyresi,marble,phyllite,etc.The intrusions in the area mainly include Haoquangou pluton,Baimawa pluton,Heishishan pluton and Fuyagou pluton.Haoquangou gold deposit is mainly formed in the Haoquangou?and ?pluton.Gold and copper mineralization is also seen in albitophyre and spilitestratum in the peripheral pluton,while distribution area of the marble is the Pb-Zn mineralized layers in this area.F1,F3 and F7 deep faults in the area are closely related to mineralization,and their derived secondary structures basically control the formation of multiple types of mineralization.Due to the alteration of the internal and external structures of Haoquangou pluton,it has become the best metallogenic and prospecting potential area of the gold deposit.The Baimawa pluton is just one of the ore-forming controlling factors of Pb-Zn mineralization.2.The representative mineralization types in the study area are mainly altered-rock type,quartz-vein type gold and hydrothermal vein-type Pb-Zn mineralization.Among them,quartz vein-type and altered rock type gold deposit have the same genesis and source of metallogenic material,but they formed by different tectonic conditions and ore-forming mechanism.The recombination of quartz-vein type and altered rock type is often seen in Haoquangou gold deposit.Altered rock type gold mineralization is mainly distributed inside the Haoquangou ? pluton and peripheral volcanic rocks,and controlled distinctly by the EW main fault;Quartz-vein type gold mineralization is widely distributed in both inside and outside of the pluton fracture,and is primarily controlled by SN fracture in Haoquangou ?pluton.3.Comparative study on the characteristics of REE of the quartz-vein type gold ore and hydrothermal vein-type Pb-Zn ore and its wall rocks shows that: There is no genetic relation between the spilite and gold or Pb-Zn mineralization;The REE composition of Haoquangou and Baimawa pluton indicates that they have the same source and magma evolution process.Quartz-vein type gold ore is homologous with granitic magma,and the metallogenic fluid is the product of the process of magmatic differentiation.Hydrothermal vein-type Pb-Zn ore source and the granite also are inherited to some extend,whose metallogenic fluid originates from magma hydrothermal but is greatly influenced by the marble,implying that the Baimawa pluton is the main ore-controlling factors of the hydrothermal vein-type Pb-Zn mineralization.Weakly positive Eu anomaly in the gold ore may indicate that the metallogenic fluid carried on the features of medium temperature and reducibility from magmatic hydrothermal.There is a little impact on the Eu in ore-forming fluid when water-rock reacted between the fluid and wall rocks.And Pb-Zn ore genesis of obvious negative Eu anomaly indicates the metallogenic fluid may be low temperature fluid,and partial oxidation mineralization environment.Its mineralization is a result of magmatic hydrothermal and marble mutual influence.4.The analysis of the geological and geochemical characteristics of the deposit shows that: the gold mineralization are closely related to the Haoquangou pluton as well as the derived dykes,which is the geological metallogenic body;The metallogenic structure or structural plane mainly are EW oriented and SN faults in which the extended area of structure and altered dykes have mineralization potential in.Altered mineral assemblages as quartz + sericite + pyrite,jarosite + kaolinite + gypsum and carbonatation are the characteristics marks of metallogenesis,which represent different ore-forming mechanism and metallogenic environment.Geological metallogenic bodies of the hydrothermal vein-type Pb-Zn mineralization are Baimawa pluton and marble;Metallogenic structures or structural planes are fractures within Baimawa pluton,tensional fault within marble,and contact zone of the spilite and marble;Barite and carbonation represent the characteristics marks of metallogenesis of the Pb-Zn mineralization,the signature mineral assemblage of which are quartz + calcite + barite.5.Tectono-litho geochemistry survey is based on the geological mapping scale in 1:10000.The study of the distribution characteristics of 19 trace elements shows that each element in the area is approximately obeying the lognormal distribution.Au,Ag,Cu,Pb,Zn,W,Mo,Bi are extremely unevenly distributed in the region,with obvious geochemical anomalies.The use of traditional iterative methods to determine the elemental background values and the lower limit of anomalies is a good reflection of the mineralization information in the study area.The location of single element anomalies coincides with the height of known deposits or mineralized sites,and the Au,Cu,Pb and Zn high anomalies have prospects for further exploration.The Au-Ag-Cu-Mo-Bi and As-Sb-Pb-Zn elements have good suitability.The first one is the indicator element combinations of gold mineralization and the other is of hydrothermal vein Pb-Zn mineralization,And the place where both are abnormal is the prospecting potential.6.Interpretation of geophysical results show that: Though the high-precision ground magnetic anomaly is a little identical with physical parameters of the ground geological mass,it can reflect the distribution of fractures in this area.So there is some significance to fractures interpretation.As for induced polarization intermediate gradient survey,the distribution area of marble and Pb-Zn mineralization are characterized by high resistivity and polarizability,while the gold ore bodies controlled by structures and alteration have the features of low resistivity but high polarizability.And the high polarizability area is consistent with mineralization area in induced polarization intermediate gradient profiles.Consequently,the induced polarization intermediate gradient anomaly could be an important prospecting indicator.7.Based on the summary of geological conditions,geochemical and geophysical exploration results,the comprehensive information prospecting model in Haoquangou mine area is built.Combined with the geological,geochemical and geophysical prospecting information in the study area,two prospecting target area and two prospecting beneficial area are delineated respectively in this paper.