Metallogenic Setting And Metallogenesis Of Nonferrous-precious Metals In Northern Da Hinggan Moutain

The northern segment of Da Hinggan Mountain is an important metallogenic beltof nonferrous-precious metals in the northeast, and even more, the whole China. Themetallogenic belt is located in the eastern segment of Mongolian-Hinggan compositemega-orogenic belt, which is located between the Erqisi-Suolun-Heihe andMongolian-Okhotsk suture zones. The northern segment of Da Hinggan Mountain consists oftwo massifs, one accretional orogenic belt, and one basin, i.e. Erguna massif in west, NorthXing'an block in east, Erlunchun accretional orogenic belt of middle Late Paleozoic era inmiddle, and Upper Heilongjiang basin in north. The studed area belonged to the continentalmargin accretional belt of southern margin of Siberian plate in pre-Mesozoic, whilesuperimposed by the continental marginal activizing belt of marginal-West Pacific tectonicdomain, with extraordinary complicated tectonic settings. The basic geological problems,such as the nature of the Erguna massif, the evolutional history of Paleo-Asian Ocean and theHinggan-Mongolian orogenic belt, the geodynamic background of Mesozoic volcanic rock innorthern segment, the influence of Mongolian-Okhotsk orogenic belt on Mesozoic tectonicevolution in Northeast China, etc. have long attracted the attention of geologists both atdomestic and abroad, which still need futher study today. The study of fundamental geologyis poor, without a comprehensive and accurate judgement about regional metallogenicgeological setting. Meanwhile, there are different ideas about the genetic types and essentialfeatures of deposits. These have severely affected reconnaissance survey and prospecting.Therefore, the prospecting have not got significant achievement for many years. For theabove-mentioned reasons, the author chose the northern segment of Da Hinggan Mountain asresearch area of doctorial paper. The author will sum up the metallogenic regularities, directprospecting and exploration of nonferrous-precious metals in research area by studies ofmetallogenic settings and typical deposits.The author took tectonic-magmatic activity and mineralization as the key, to studysystermatically lithology, petrochemistry, geochemistry and isotope geochemistry of variousintrusive rocks and Mesozoic volcanic rock in north Da Hinggan Mountain. Many newgeochronological data by SHRIMP zircon U-Pb, 40Ar-39Ar, and Rb-Sr isotime line have beenobtained for the metamorphic rocks of Xinghuadukou Group, every epoch typical intrusions,and Mesozoic volcanic rocks in the studied area. On the basis of detailed field investigationon the typical deposits, we studied the fluid inclusions of the typical deposits, and obtainedthe mineralization temperature, salinity, pressure, and depth of the typical deposits in thestudied area. Meanwhile, we analyzed the rare earth elements and trace elements of rocks (orores) and geological bodies from the typical deposits and different geological stages, anddetermined the main source beds. Based on the isotopic data of S, H, O, and Pb, the authorascertained the source of ore substances, nature of ore-forming solution, and genetic types ofdeposits. On the basis of metallogenic regularity, metallogenic model and prospecting criteriaas well as the data of geology, geophysical exploration, geochemical exploration, remotesensing etc. The author discussed the prospecting potential in the northern segment of DaHinggan Mountain.A series of high precision geochronological data (2600 Ma±, 2400～2600 Ma, 1888±85 Ma, 892±20 Ma, 504～517 Ma, 450 Ma±, and 193～215 Ma) by SHRIMP U-Pb datingof zircons have been obtsind for the metamorphic rocks and granitoids in the northernsegment of Da Hinggang. The geochronological data showed that there were crystallinebasements of Neoarchean-Paleoproterozoic in the studied area.The basement nature of theErguna massif which has long disputed has been solved. The age of 1888±85 Ma wasconsidered as the age of an important tectonic-hydrothermal event in late Paleoproterozoicwhich represent Xingdong movement, and the age of 892±20 Ma was the age of an regionalmetamorphism. At the same time, the Rodinia supercontinent was formed in the southernmargin of Siberian platform. The discovery of post-collsional granitoids of 504～517 Masuggested that Salair orogenic movement was finished with closured of the north branch ofthe Paleo-Asian Ocean ca. 500 Ma ago. We suggestd that an important magmatic intrusiveevent occurred in 404±15 Ma. Island arc and syncollisional granitoids of 193～251 Ma arepre-orogenic and synorogenic granitoids of the Mongolian-Okhotsk orogenic belt, theirgenesis were closely related to the evolution of the Mongolian-Okhotsk orogenic belt innorthern part of the studied area. Based on high precious geochronological data of SHRIMPzircon U-Pb dating, in view of the features of petrology, petrochemistry, geochemistry andisotope geochemistry, the tectonic evolutions of the northern segment of Da HingganMountain can be roughly divided into 10 stages, i.e. (1) the ancient land massif stage, (2) theErguna massif forming stage, (3) the primary cracking stage of the massifs, (4) the Rodiniasupercontinent forming stage, (5) the cracking stage of Rodinia supercontinent, (6) theXingkai-Sarair orogenic stage, (7) the cracking stage of the Paleo-Asian Ocean, (8) thePaleo-Asian Ocean closing and orogenic stage, (9) the Mongolian-Okhotsk orogenic beltforming stage, and (10) the evolution stage of intracontinent.The geochronological data from 40Ar-39Ar and Rb-Sr isotime line suggested that theMesozoic volcanic rocks in northern part of Da Hinggan Mountain were formed in 130～116.7 Ma, which belong to Early Cretaceous period. The characteristics of major, REE andtrace elements of the Mesozoic volcanic rocks indicated that Tamulangou Formation wasformed in a transform setting of intracontinent from compression to extension, and related tothe collision-super collisional orogenic processes of the Mesozoic Mongolian-Okhotskorogenic belt. The Shangkuli Formation volcanic rock was characterized by those of islandarc, which was affected by Izanaqi plate inclined subducting, and converged beneath theAsian continent. The Yiliekede Formation volcanic rock was formed in an extensionalbackground of intracontinent. In a word, the formation of the Mesozoic volcanic rocks in thearea was closely related to the orogenic process of the Mongolian-Okhotsk orogenic belt, butnot immediately related to the westward subduction of the Pacific plate. The volcanic rockswere probably resulted from the thickened crust, and delamination of lithosphere.Based on study of the typical deposits of Chaganbulagen Pb-Zn-Ag deposit, Shabaosigold deposit, Wunugetushan Cu-Mo deposit, Erentaolegai Ag deposit, etc., the deposit typesof nonferrous-precious metals in the area can be divided into 7 genitic types, i.e.hydrothermal vein Pb-Zn-Ag, orogenic gold, porphyry Cu-Mo (Au), epithermal Au-Ag (Cu),SEDEX Fe-polymetallic ore, skarn Cu-polymetallic ore, and skarn and meso-hyperthermalvein composite type of W-Sn-Mo-polymetallic ore deposits. The mineral species weremainly Pb, Zn and Ag, followed by Au, Cu and Mo. The metallogenic epoch ofnonferrous-precious deposits was Variscan and Yanshanian, major metallogenesis focused onYashanian.The study of fluid inclusions of the typical deposits showed that the ranges ofmineralization temperature of hyperthermal vein Pb-Zn-Ag, orogenic gold, porphyry Cu-Mo,and epithermal Au-Ag (Cu) deposits are 261.4℃±, 266.5～295.2℃, 333.6℃±, and 200～260℃, respectively. The mineralization temperatures, from high to low are presented atporphyry Cu-Mo (Au) deposit, orogenic gold deposit, hydrothermal vein Pb-Zn-Ag deposit,and epithermai Au-Ag (Cu) deposit. The salinities of ore-forming solution of thehydrothermal vein Pb-Zn-Ag, orogenic gold, and epithermal Au-Ag (Cu) deposits are all inlow level, ranging 2.23～7.05 wt% NaCl, 2.06～11.23 wt%, and 1.73～5.80 wt%,respectively. The porphyry Cu-Mo (Au) deposits have a wide range of salinity (3.76～50.52wt% NaCl), indicating that there were two stages of solutions, and these deposits probablyexperienced the early stage of porphyry Cu-Mo of meso-hyperthermal and high salinity, andthe late stage of mesothermal and low salinity gold mineralization, respectively. Themetallogenic pressure ranges of the orogenic gold deposit are 54.11～92.73 MPa, withmineralization depths of 5.88 and 7.68 km. The metallogenic pressures of the hydrothermalvein Pb-Zn-Ag deposit and epithermal Au-Ag (Cu) deposit are 21.30 MPa and 17.93 MPa,respectively, mineralized are 2.13 km and 0.60 km in deep. The metallogenic pressures of theporphyry Cu-Mo (Au) deposits are between 64.50 and 114.60 MPa, with mineralizationdepths between 2.15 and 3.82 km. The metallogenic depth sequence of main deposit types inthe northern segment of Da Hinggan Mountain are the the orogenic gold deposit, porphyryCu-Mo (Au) deposits, hydrothermal vein Pb-Zb-Ag deposit, and epithermal Au-Ag (Cu)deposits from deep to shallow, in turn. The value of sulfur isotope (δ34S) of thehydrothermal vein Pb-Zn-Ag deposit, orogenic gold deposit, porphyry Cu-Mo (Au) deposit,epithermal Au-Ag (Cu) deposit, and skarn and meso-hyperthermal vein composite typeW-Sn-Mo-polymetallic ore deposit are -14.1‰～5.4‰, -5.2‰～9.6‰, 1.1‰～3.9‰, -12.2‰～-6.4‰, and -2.9‰～2.6‰, among which the range of 0.0‰～6.0‰ is predominant.The characteristics of sulfur isotope (δ34S) indicated that the origin of sulfur was closelyrelated to anatectic magma, but the value of δ34S from some epithermal and hydrothermalvein deposits (e.g. Siwumuchang gold deposit and Xijinuoshan Pb-Zn-Ag deposit) are farbellow 0‰, which suggested that the sulfur come mainly from host rock or sedimentary rock.The characteristics of H and O isotopic compositions of the deposits showed that theore-forming solution is mainly composed of magmatic water mixed with meteroric water.The heat source were derived from the Mesozoic volcanic-invasive magma. The lead isotopiccomposition of the deposits reflected the characteristics of orogenic lead isotope, and the leadof ore came mainly from the Mesozoic igneous rocks.The northern segment of Da Hinggan Mountain is an important metallogenic provinceof Pb-Zn-Ag deposits. The analysis data of ore-forming trace elements showed that thecontents of Pb, Zn and Ag in all rocks of each epoch are high. The content of gold is higherin the Paleoproterozoic Xinghuadukou Group, Neoproterozoic Jiageda Formation,Lower-Middle Devonian Niqiuhe Formation, and Upper Jurassic Tamulangou Formationthan the average value in the crust or the same rocks in the world. These strata wererecognized as the source bed for gold deposit in studied area. The Lower Cambrian ErgunaheFormation and Lower-Middle Ordovician Duobaoshan Formation were regarded as thesource bed of Cu-Mo deposits. The Xingkai-Salair granitoids were favorable intrusive rocksfor the forming of Ag, Cu, Pb, Zn and Mo deposits. The Variscan-Indosinian granitoids werefavorable intrusive rocks for Ag, Pb, Zn and Mo deposits. The Yanshanian intrusive rock wasore-forming mother rock for Au, Cu, Pb, Zn and Mo deposits.According to the theory of metallogenic series of deposit, the author worked out 5deposit metallogenic series with 20 deposit types in the northern segment of Da HingganMountain, namely, (1) the metallogenic series of SEDEX deposits related to the revolution ofLate Paleozoic volcanic-sedimantary basin, (2) the metallogenic series of Fe-polymetallic oredeposits related to the intermediate-acid invasive magma in Late Paleozoic era, (3) themetallogenic series of Au, Cu, W, Sn, Mo and polymetallic ore deposits related to thecontinental-continental collision between the North China and Siberian plates in Mesozoicera, (4) the metallogenic series of Pb, Zn, Ag, Cu and Au deposits related to theintermediate-acid intrusive rock of intraplate in Mesozoic era, and (5) the metallogenic seriesof Au, Ag, Cu, Pb, Zn and Mo deposits related to the Mesozoic volcanic-subvolcanic rocks,and hypabyssal porphyry in intraplate.On the basis of the metallogenic setting, ore-control structure, mineralization etc., thestudied area can be divided into 3 metallogenic belts and 12 metallogenic subbelts, i.e. (1) theDerbugan Pb, Zn, Ag, Au, Cu, Mo and U metallogenic belt in the Yanshanian, (2) theTayuan-Wunuer Fe-polymetallic metallogenic belt in the Variscan-Yanshanian, and (3) theYanshanian Au, Cu, W, Sn and Mo metallogenic belt in the southeastern margin of theMongolian-Okhotsk orogenic belt. Study showed that the Derbugan metallogenic beltproposed by previous researchers cann't comprehensively reflect the characteristics ofmetallogenesis in this area. The author thought that there are 3 obviously differentgeodynamic rigems from Paleozoic to Mesozoic era. Correspondingly, 3 metallogenic beltsof different epochs, different mineral species and different genetic types were formed. (1)The Tayuan-Wunuer Fe-polymetallic metallogenic belt in the Variscan-Yanshanian wascontrolled by the Paleo-Asian Ocean geodynamic rigem. Its metallogenesis in Late Paleozoicera was related to the splitting and orogenesis of the Paleo-Asian Ocean. In EarlyCarboniferous, VHMS type of Fe-polymetallic ore deposit was formed in the metallogenicbelt, subsequently, forming skarn type Fe-polymetallic ore deposit in collisional andpost-collisional stages of the Late Variscan. (2) The metallogenic belt of the southeasternmargin of the Mongolian-Okhotsk orogenic belt was formed in Mesozoic era, under themetallogenic background of collision-post collision. In the belt, the orogenic gold deposit,and skarn and meso-hyperthermal vein composite type W-Sn-Mo deposits were usuallygenerated. These deposits were generally related to acid-ultraacid granitoids of late orogeny.Their metallogenic epoch focused on Late Jurassic (135.6～150.9 Ma). (3) The Derbuganmetallogenic belt is an important Pb, Zn, Ag, Au, Cu, Mo and U metallogenic belt, whosemetallogenic epoch focused on Early Cretaceous (120 Ma±). These deposits were formed inextensional environment of intraplate, with main types of hydrothermal vein Pb-Zn-Agdeposit, porphyry Cu (Mo) deposit and epithermal Au-Ag (Cu) deposit, closely related tocontinental volcanic-subvolcanic rocks of Mesozoic era.On the basis of study on the basic geology, typical deposits and metallogenic series ofdeposits above-mentioned, the metallogenc model and prospecting criteria were set up in thestudied area. Finally, based on the data of geology, geophysics, geochemistry, remote sensingetc., as well as the GIS-based mineral resources database, the author ascertained theprospecting potential of Au, Ag, Cu, Pb, Zn and Mo in the studied area, and pointed outfavorable metallogenic region and district, meanwhile, worked out 15 prospective areas and24 prospecting targets. In addition, the author classified the prospective areas with grade A, Band C in turn according to their prospecting potential from high to low. These works havelaid a foundation for subsequent reconnaissance survey and prospecting.