Geochemical Fields Of Metallic Deposits In West Qinling

Under the guidances of Orogenic Metallogeny, Geochemistry, and Self-Organized Criticality, and on the basis of previously basic geology, geology of mineral resources, and the data of regional geochemistry and mineral geochemistry, this paper had given a systematic state and acquired a number of results about a series of topics in west Qinling, such as composition of all geological units, metallogenic regularities, geochemical processes of ore-forming, patterns of geochemical fields of metallic deposits, geochemically metallogenic forecast models of mineral deposits, and large-middle scale of forecast models of typical ore deposits.1. Regionally geological backgrounds1.1 The compopsitions of strataSome strata, such as Qinling Gr, Jixian System, Qinbaikou System, Danfeng Gr, meso-Silurian Zhouqu Fm, meso-Devonian Shujiaba Fm, meso-Carbonaceous combined Xiajialing-Dongzakou Fm, have diversified compositions in which there are basic elements from depth, clastic elements from continents, and the elements from hydrothermal sediments. Upper Palaeozoic Erathem in mid-Qinling is richer in the assemblage of evaporate, and has characteristics of critical mineralization of the element Pb, Hg, and Cd. South Qinling has that of the element Fe, Mn, Zn ,Mo, and Ba. Since Neoproterozoic Era, organism had anticipated in the processes of part of strata.1.2 The compositions of intrusive rocksJinning intermediatie-basic intrusive rocks are rich in the metallogenic elements Cu, Pb, Zn, Ni, and Fe. Caledonian intermediate rocks are rich in the elements from hydrothermal alteration, most of which are rich in HFSE, and part of which are rich in compatible elements. Indosinian quartz monzonite and Wenquan granites are rich in compatible elements, and the monzonitic granites of the same ages such as Baijiazhuang rock mass are rich in alkaline elements as Nb, K, and Y. The Yanshanian rock mass in western section of mid-Qinling are rich in Ferrous group elements, and that in the eastern section are rich in lithophile elements and thiophile elements.1.3 The crustal evolvement and deep structuresOn account of the strata with their diagram of claster analysis from immobile element, their diagram of La/Y—La/Co, and their ratio of La/Th, the intrusive rocks with their diagrams of R1-R2 and Nb-Y , the lithospheric tectonic, and previous points of view, it was thought that, the granitoid formed from Caledonian to Devonian were probably the durative responses to early Jinning convergency of Yangtse plate and north China plate. From early Devonian to Mesozoic, Yangtse plate and north China plate had gradually converged companied by shrinking of Mianlue ocean, the collided point had migrated from east of Devonian to west of Mesozoic until incontinental orogenesis of Mesozoic occurred. The magmatism in mid-Qinling and involved mineralization since Mesozoic were related to tectono-thermal erosion from subducted and ruptured Songpan plate. The Yangba Fm of Jixian System and Yangtianba Fm of Qinbaikou System in Bikou Gr didn't outcropped there until Indosinian movement.2.Metallogenic regularities2.1 Metallogenic agesThe statistics about metallogenic ages showed that, the peak period of sedimentary mineralization was Silurian and Devonian, in which was principally meso-late Silurian and meso Devonian. The hydrothermal mineralizations occurred mainly after Carbonaceous in which peak period of mineralization was Triassic and Jurassic. Behind veins mineralizations didn't always lagged, but lagged 10 Ma later behind faults functioned.2.2 Mineral distribution in spaceBy making use of mineral space information, 7 concentrational areas, such as Xiahe, Lintan, Dangchang, Wudu, Liziyuan, Chengxian, and Faziba, are delineated, of which the Chengxian area presents itself as the maximum in area and intensity, and subsequently the Lintan and Xiahe. In tectonic units, the mid-Qinling takes the maximum of concentrational areas.A large amount of deposits or occurences stand in the range of 0-10Km away from deep faults, most of which in the range of 5Km away from intrusive masses, and most of which occur in the range of 6Km away from each other and has a plannar distribution model. The distances from deep faults, intrtusive masses to deposits or occurences, and from deposits or occurences each other are respectively characterized by multifractals.2.3 Metallogenic series and metallogenic system of metal mineral depositsA rule for compartmentalizing metallogenic series was concretely set up on the basis of concept of metallogenic series defined by Chen Yuchuan, and eventually all metallic mineral deposits were divided into 10 metallogenic series, 13 sub-metallogenic series, and 30 types, in which there are 3 for iron, 2 for iron, copper, and multimetals, 2 for copper or molybdenum, 1 for lead and zinc, 1 for mercury and antimony, and 1 for gold.Also was concretely set up a rule for compartmentalizing metallogenic system on the basis of concept of metallogenic system defined by ZHAI Yusheng, and finally the metallogenic system in west Qinling were divided into 6 big clasters of metallogenic system, 9 clasters of metallogenic system, and 11 metallogenic system.2.4 The growing processes of mineral resourcesThe facts of tonnage to grade of mineral resources can be fitted by exponential and linear functions, double logarithm plots of tonnage to grade and that of orebody resources consist of 3 or 4 line sections, and deductive results from maths born out that, the equation of tonnage to grade of mineral deposits can be described as exponential equation from linear addition of nonlinear multiplication processes.3. Geochemical processes of ore-forming3.1 Physical and chemical qualifications of ore-formingThe metallogenic temperatures of subvolvanic hydrothermal subseries of molybdenum ores were 160-180℃; those of hydrothermal sediment series of lead-zinc ores and hydrothermal series of gold ores were all between 60℃and 480℃, but the concentrative temperatures of lead-zinc series of ores and hydrothermal series of gold ores were 80-120℃and 150-300℃respectively; and those of sedimentary manganese ore series were 25-32℃.With the help of MRK equation of CO₂ system, and the relation of salty, density, and temperature to pressure of NaCl-H₂O system, the lithostatic pressures estimated are all within 1 Km, that of reconstructed ores were generally higher than that of sedimentary ores but reconstructed ores acompanied by abrupt decompression and exsolution processes. The ranges of pH and Eh of diversified ore deposits are positively correlative to their amount of ore deposits or occurrences.3.2 Geochemical processes of ore-fomingFrom the composition of ore and metallogenic fluids, and the physical and chemical qualifications of minerlalization, the geochemical processes of mineralization of different genesis of metallic ore deposits, concretely, that of iron, manganese, copper, leadand zinc, gold, mercury, and antimony, had been described. The metallogenic processes varied with metals and metallogenic subseries.The geochemical fields of 39 elements are characterized by their multifractals, which wre further divided into single concentration, double concentrations, triple concentrations, fourfold concentrations, and quintupling concentrations, and the large-mid size of deposits were all from more than triple concentrating processes.4.Patterns of regionally geochemical fieldsThe patterns of metallic geochemical fields, i.e. that of iron, manganese, copper, lead and zinc, gold, mercury, and antimony, were depicted from the angles of linearity and nonlinearity. Generally, though the compositions of geochemical fields vary with elements, the pattern parameters of which present themselves analogous to each other, for examples, the places where ore deposits stand are anomalous areas of moderate contents, and don't correspond to anomalous peaks except few ore deposits; the varied extents of semivariogram are between 0.7 to 0.9 with the characteristics of random fields; the static pattern entropies in the orientation from south to north are less than that from east to west, and Brown Fractal Dimensions are just inverse, that indicate the variations from south to north are more complicated; almost all ore deposits locate in the zones where the singular indexes are less than 2.0, especially that of lead, zinc, gold, mercury, and antimony are generally less than 1.8, and that proved the singular index is effecvtive to contour metallogenic areas of different kinds of mineral resources.The Lyapunov indexes of geochemical fields of part of metallic deposits showed that, the regionally geochemical fields of Pb and Zn are characterized by their criticalities, that of soluble elements as Cu and Mo tended to be stabilized patterns, and man-made pollutions made geochemical fields of Hg and Sb have the characteristics of chaos.5.Regioinally geochemical Models for metallogenic prognosisAbout effective estimation of modeling methods showed that linear regression is quite effective, with capability of discriminating of different size ore deposits, the secondary is logical information method, the third is reconstruction of factor model method, and the Evident Weight method gave a reasonable metallogenic assemblage but gave a bad verified result. Finally, 14 regionally geochemical models for prospecting were found by the method of linear regression, they are that of sedimentary iron deposits, sedimentary and metamorphosed iron deposits, weathering and leaching iron deposits, sedimentary and reconstructed manganese deposits, skarn copper deposits, porphyry copper deposits, hydrothermal copper deposits, VMS copper deposits, sedimentary lead-zinc deposits, reconstructed lead-zinc deposits, magmatic hydrothom type of gold deposits, sedimentary and reconstructed gold deposits, mercury deposits, and antimony deposits.6. Large scale of geochemical models and the problems of renormalization for prospecting6.1 Primary halos of Daijiazhuang lead-zinc ore depositThe zoning formed in sedimentary mineralization is, from centre to outside, Fe-Au-Bi-Sr-W-Cr-Pb-Hg-Co-Sb-Ni-V-Mo, respectively that means from hydrothermal sediments to normal sediments under reduction.The zoning formed in reconstructed mineralization is, from centre to outside, Cu-Zn-Mo-Pb-Sn-W-Hg-Ni-Co, respectively that means from multi-metallic elements to hydrothermal construction composition.Lyapunov indexes showed that, Hg from meso-low temperature mineralization has self-organized criticality in both time and space, and meso-high temperature composition as Cu, Zn, and Bi have self-organized criticality while behave stabilized geochemical pattern.With the combined index [PB*W]/Cu², and its fitted power function, deep resources prediction model, which has a high proportion of variance and a high fitted level, was acquired.6.2 Pedogeochemistrical halos of Daijiazhuang lead-zinc depositThe zoning calculated by zoning index method is, from centre to outside, Sn-Cu-W-Mo-Ag-Zn-Pb-As-Sb, which is consistent with hydrothermal deposits.Lyapunov index showed that, the processes of soil-forming made geochemical fields of most of metallogenic elements stabilized, but the power spectrum of elements in soils inherited to that in rocks.A mathematic prediction model which is varying with the area of Ag anomalies, was set up, and ideally verified.6.3 Geochemical halos of stream sediments in the scale of 1:50000Lyapunov indexes, and 1/f phenomina in frequent domain indicated that, fluviation in the surface would make some elements with stabilized pattern in primary halos tend to be ctritical or of chaos, bring about anomalies irrespective to mineralization, and complex stream sedimentary anomalies for prospecting. Metallogenic elements and their indicator elements present excursion to 1/f phenomena in the low frequency, individual element as Cu behaves out-of order in frequent domain, all these show us its complicated genesis and unreliable of applying its data to resources evaluation.The combined anomalous map of multi-elements showed a zoning centered on Pb, and from centre to outside is Pb-Cu-Zn-Mo-As-Hg-Ag. The Pb anomalies presents a ringed zoning model with centering on Daijiazhuang lead-zinc ore deposit and being vertical to the trend of strata in NEE orientation, that imply these ringed anomalies were derived from reconstructed mineralization.On the states of geochemistry and self-organized criticalities of metallogenic elements and their indicator elements under the surface, selecting areas of Pb, Zn, As, Sb, and Hg as variables, which are affinitive to mineralization and more stable, prediction model for prospecing was set up, and well verified.6.4 The problems of renormalization in mineral explorationBy research of the problems of renormalization in mineral exploration, we thought that, in the 3 explorative scales of 1/200000, 1/50000, and 1/10000, the explorative engineering should be extended respectively to about 6.5Km, 0.16Km, and 0.002Km. While the frequency of anomalous data is less than 10%, which has few influences on correlative length, and it is the scale that play a decive role to correlative lengths.