Metallogenic Prediction Based On Synthesis Information For Endogentic Gold Deposits In Huma-Mohe Area, Heilongjiang Province

Huma-Mohe area in Heilongjiang province is a part of the Inner Mongolia-Daxing'an mountain metallogenic belt. Regional metallogenic study reveals that precious and base metals such as lead and zinc resources in the area are with great potential. The main factors that restrict the deposit discovery are the unclearness of pre-Mesozoic geotectonic evolvement, pre-Cambrian basal characteristics, linear and annular structures controlling metal mineralization, Mesozoic magmatic activity, and metallogenetic mechanism and conditions.In this paper, most methods for metallogenic prediction are reviewed. The theoretical foundation and characteristics of metallogenic prediction based on synthetic information are discussed. Geophysical information from aeromagnetic surveying, gravity prospecting and remote sensing is studied and interpreted. The geophysical characteristics of pre-Cambrian basal metamorphic rocks, Paleozoic and Mesozoic formation are summed up. The distribution of Pre-Cambrian basal rocks, basal structural framwork and evolution and regional magmatectonic activities are found out. The geophysical prospecting indicators of endogenesis gold deposits are also summarized.The structures in the area mainly trend east-west or northeast, controlling the spatial distribution of magmatic rocks, with characteristics of multiperiodic activity and distributed in the margins of the pre-Cambrian basements. The associated or derived faults trend westeast or northeast, directly controling Au-mineralization. The turning, combination and crossing of the faults are favorable for metallogenesis.The petrologic, geochemistry and geophysical characteristics of intrusive rocks in the area are studied. The granites formed in every period are divided into four series, which are gneissic granite, diorite-granodiorite-admellite, admellite-potassic granitealkali feldspar granite, and alkali-granite. The controlling rule to gold deposits of intrusive rocks is discussed. The granite bodies in the area are divided into inheritable and non-inheritablebodies. The inheritable granite body is favorable for metallogenesis of gold deposits.Structural geochemistry indicates that headwater catchment basins of gold placer are controlled by reveal and/or hidden pre-Cambrian base. The basal rocks, Mesozoic volcanic rock sand granitic intrusive rocks are the main suppliers of metallogenetic materials to placer gold deposits. The endogenetic gold deposits are closely associated to gold placers, and laid in the headwater or side stream of catchment basins. The ascending catchment basins are favorable to endongenetic gold deposits, and degressive catchment basins are perspective area to forming gold placers.There are six Au-mineralizatiqn concentrative areas in Huma-Mohe area. The metallogenetic characteristics of concentrative area are discussed respectively. The genetic types of endogenetic gold deposits are divided into magmatic hydrothermal deposit involved intrusive and hidden hydrothermal deposits, and volcanic-subvolcanic hydrothermal deposits. The mineralization characteristics of both types are discussed. The genetic models of gold deposits are established on metallogenetic conditions and rules.Metallogenetic series of endogenetic gold deposits on synthetic information are classified into metamorphic series, terrestrial volcanic series and intrusive magmatic series. The mineralization characteristics of each serie are generalized. The prospecting models for metallogenetic series are established. The information characteristics of 14 prospecting areas are summed upwith 8 targets of grade I and 6 targets of grade II defined. The metallogenetic favorability indexes are evaluated for the factors of the pre-Cambrian basal rocks, Paleozoic cover and Mesozoic cover, the annular and linear structures interpreted from information of aeromagnete gravity. The pre-Cambrian basal rocks are exclusive to Au-mineralization. The main controlling conditions of gold deposits from synthetic information are large-scale annular and linear structures, the pre-Cambrian basal rocks, Indosinian and Yanshanian magmatic and volcanic activities, etc. The favorable positions for gold deposit are Mohole steep gradient zone, the plate or basal block margins, the conjunction of geotectonic elements, the margins of acid-intermediate magmtic bodies, and the crossing of faults.Synthetic information thirteen perspective signs on synthetic information are:(1) Gradient zone of gravity anomaly around reveal or hidden pre-Cambrian basal rocks.(2) Aurum compositive geochemical anomaly zone distributed in auriferous granitic bodies or the contact rocks formed in various epoch or phase.(3) The contact confines of different geotectonic elements.(4) The various gradient antitone structures and cross points of various orientational faults.(5) The gentle inclining face or tilting segment of auriferous granitic bodies.(6) The interfaces between the reveal and/or hidden pre-Cambrian basal rocks and the terrestrial volcanic rocks.(7) The remote sensing circular features superposed with the zero lines of the vertical second derivative of geomagnetic and gravity field.(8) The antitone transmission faults and associated circular and linear geochemistry anomaly.(9) The antitone structures and the circular and linear gradient zones of various magnetic anomaly.(10) The subvolcanic rock and the svolcanic conduit bodies and associated circular geochemistry anomaly.(11) The geochemistry anomaly and antitione anomaly superposed with linear and circular geochemistry anomaly.(12) The anomaly of aurum compositive geochemistry distributed in the subcatchment basins of headwater catchment basins of gold placer.(13) The concentration of gold deposits and aurum geochemistry anomaly.The directly perspective signs of endogenetic Au-mineralization are gold placer, though the source of metallogenetic materials of gold placer are not mainly endogenetic gold deposits, according to the quanlitative prognosticating for gold placer reverses. The geologic conditions for gold placer are favorable to endogenetic gold deposits as well. The auriferous geological bodies that provided abundant materials for gold placers are the key metallogenetic condition for endogenetic gold deposits. The forming and evolving process of auriferous geological bodies offered favorable condition to Au-mineralization. There is a evolving and inheriting relation between endogenetic gold deposits and gold placers.Fourteen targets minerogenetic prospect provinces are predicted depending upon elimination of pivotal element and sum of squares. The reliabilities of these targets are validated respectively. The quantitative prediction for reserves of endogenetic gold deposits is actualized with that adopted the method of logic information combining element analysis to logic numeration. The total reveres of endogenetic gold deposit is 1268,000 kilogram, including 666,500 kilogram of grade I , 185,500 kilogram of grade II, 416,000 kilogram of grade III .Based on the regional metallogenetic condition, the prospecting models of Au-mine-...