Yanshan area includes north Hebei Province and west Liaoning Province wherepreserve zany famous large-middle scale voluable gold, silver, copper, lead, zinc andmolybdenum deposits in China. Because Yanshan area lotates in the east inner part ofEurasia continental prate in Mesozoic era, its Mesozoic orogeny and mineralizationcaused by strong crustal movements are very special and typical. The studies ofMesozoic tectonic evolution, time-spatial distribution of gold-silver-multimetaldeposits and their relationships in Yanshan area are very important geologicalresearch program which has been attracting the attentions of generations of geologists.Though great progresses have been made, there are still many problems that need moredetail studies.
On the basis of the former geological data and the author's research results inYanshan area, this article pay mainly attention to three items,(1). identification andanalysis of palaeostructures, geological events including activities of magmaintrusion, volcanic eruption, uplifting and depression of basin, sedimentation,palaeostress field and the deformational enviroment in each period of Mesozoic era, (2).the dating and spatial distribution of the important types of gold-silver-mutimetaldeposits; (3). the relationship between regional tectonic activity and mineralizationof gold-silver-multimetat. Many effective methods have been used, such as the isotopicdating for the faults and deposits, statistic analysis for time-spatial distributionof regional structures and mineralization, etc.
Ⅰ. General Skeleton of Regional Geology and Tectonics in Yanshan Area
The oldest rocks in China, the thick and successive middle-tate Proterozoi(?)strata, the structures formed in several periods of orogeny and many structure systemsexist in Yanshan area.
1.Regional strata system
There are Archean -early Proterozoic metamorphic strata, middle-late Proterozoicsedimentary rocks, Cambrian-Ordovician marinal sedimentary rocks, Carboniferous-Permian sedimentary rocks mainly formed in shollow and marginal sea, Mesozoiccontinental volcanic-sedimenlary rocks formed in the basins in mountainsand Cenozoic lava and sediments in Yanshan area.
The Archean-early Proterozoic metamorphic rocks originated from marinal volcanic-sedimentary and intrusive magmatic rocks which were identified as TTG rock series in recent years. The middle-Late Proterozoic strata consist of sandstone, siltstone,shale, quartzite, dolomite-Limestone and some basalt-andesite layers which were relatedto the middle Proterozoic rifting process. The Cambrian-Ordovician strata mainlyconsist of limestone and shale. The Carboniferous-Permian strata mainly consist ofconglomerate, sandstone, shale and many layers of coal. The Mesozoic strata consist ofmany rhythms of continental coarse-fine sediments and volcanic rocks.
2. Regional crustal movements
At least 7 periods of strong crustal movements developed in Yanshan area, include4 periods of orogeny in early Precambrian and 2 periods of orogeny in Mesozoic stage.
The 4 Precambrian orogenies are Qanxi orogeny, Fupin orogeny, shangshazi orogenyand Luliang orogeny. Qianxi orogeny developed in 2900-3100 Ma and is characterized bythe deep metamorphism, plastic-ductile deformation and strong magma eruption andintrusion. Fupin orogeny developed in 2400-2600 Ma and is characterized by middle-deepmetamorphism, strong magma intrusion and eruption, plastic-ductile deformation andgranitization, etc. Shangshanzi orogeny which happened near 2200 Ma is characterizedby shallow-middle metamorphism, ductile deformation, granitization and magma intrusion.Luliang orogeny which happened in about 1800 Na is the most important orogeny in northChina platform. Dutile-brittle deformation, green-schist metamorphism and magmaintrusion occurred strongly during lutiang orogrny.
The two Mesozoic orogenies are Indosinian orogeny and Yanshanian orogeny.Indosinian orogeny which developed in Triassic period marks the beginnin9 of a newstage of the crustal evolution in Yanshan area. Yanshanian orogeny happened inJurassic-Cretaceous periods is very strong and so characterized that the name of thisorogeny which is widety affected in east China originated in Yanshan area.These two Mesozoic orogenies are both marked by several regionat fold episodes, strongtectonic movements, brittle fault activities, magma intrusions and volcanic eruptions,etc.
Crustal movements in late Palaeozoic era and Cenozoic era are also much strong inparts of Yanshan area. 4 Cenozoic rift basins in Yanshan area were caused by Himalayarifting process.
3. The deep structures
Geophysics, such as the gravity, seismology, magnetism, etc. provides effectivedata for the imformation about deep structures in Yanshan area. These data show thattwo important NE-NNE trending faults and three important latitudinal faults cut theMoho discontinuity and entered the upper mantle. Other main regional NE-NNE treudingfaults and latitudinal faults entered the deep crust but did not apparently cut theNoho discontinuity. Most northwest trending faults,ε-type structure systems, circularstructures and most of the minor faults are limited in the upper crust and the surfaceof the crust.
Geophysics data cannot effectively show the figures of pataeo-deep-structure ingeological history. The pataeo-Moho-depth meter and the distribution of mantle andcrust originated granites which will be discussed in the next part in this article,can be used to analyse the depth of Mesozoic Palaeofaults in Yanshan area. The resultsfrom these two geological methods show that the general figure of deep structures inMesozoic era is similar to that in Cenozoic era. But in Mesozoic era the latitudinaldeep faults entered much deeper than in Cenozoic era and the northeast trending deepfaults in margins of Cenozoic rift basins entered deeper and deeper from Mesozoicera to Cenozoic era.
4. Regional structure skeleton
Five types of structure system exist in Yanshan area. They are Latitudinalstructure system which is mainly composed of east-west trending faults and ductileshear zones, Neocathaysian structure system which is mainly composed of northeast-northnortheast trending compressional faults, folts and northwest trending extensionalfaults,ε-type structure systems, circular structure systems and northwest trendingcompressional-shear faults. These structure systems have clear appearence in the photoof landsat Imagine and form the main regional structure skeleton in Mesozoic-Cenozoicera in Yanshan area.
The relationship between the latitudinal structure system and the Neocathaysianstructure system has been argued for long time. Some geologists concluded that. thesetwo structure systems are coexist structure systems which formed in the same regionalstress field of the same periods. Other geologists realised that the structure systemsformed in different deformational enviroment and different stress fietd, theNeocathaysian structure system formed much later than the latitudinal structure systemand often cut the east-west trending structures. This article supports the laterconclusion by the data of the translation of Landsat Imagine, the field observationfor the spatial relationship between the two groups of structure systems, (?)sof Palaeostress field analyses in different stages.
Ⅱ. Mesozoic Crustal Movement and Its Related Geological Events in Yanshan Area
Yanshan area located 1000 km away from the deducted zone of the Pacific Plateand was one of the east parts of Eurosia continental plate in Mesozoic era but thecrustal movement and the tectonic activity in Mesozoic era in this area are verystrong. Prof. Cui called the Mesozoic inner continental orogeny in Yanshan area theYanshan type orogeny which is distinguished from the types of orogeny locate betweentwo plate boundaries. The general characteristics of the Mesozoic crustal movement andits related tectonic events in Yanshan area will be discussed in this paragraph.
1. The stages and fold episodes of Mesozoic crustal movement.
There are two regional Indosinian fold episodes and four regional Yanshanian foldepisodes in Yanshan area. They are Indosinian fold episodeⅠ,Ⅱand Yanshanian foldepisodeⅠ-Ⅸwhich are widely and strongly developed in the east Eurosia continent.
The Mesozoic tectonic evolution in Yanshan area can be divided into 4 stages: the earlyIndosinian stage, the late Indosinian stage, the early Yanshanian stage and the lateYanshanian stage.
2. Mesozoic volcanic-sedimentary rock series, the space distribution of upliftsand depressions and their mathematic model.
The Mesozoic volcanic-sedimentary rock series in Yanshan type Inner continentalorogeny are distinguished from rock series in other types of orogenies. In Yanshanarea, Mesozoic Molasse-like rock series, coal-bearing and locustrine face sedimentaryrock series were widely distributed in the Mesozoic basins among mountains. The Molasse-likerock series are the mixture of angular pebbles, coarse sands and siltstone, whichresulted from the unbalance vertical crustal movements. In cross section the threesedimentary rock series occurred in rhythm.
In Yanshan area, the Mesozoic volcanic eruptions are very strong, which formed atleast 2 periods of Indosinian volcanic rocks and 5 periods of Yanshanian volcanicrocks. The volcanic rock series varied from basalt series-andesite series-acidvolcanic rock series and show rhythm in vertical occurrence.
Most of above sedimentary rock series and volcanic rock series distributed inMesozoic little-middle scale mountain basins in Yanshan area which are departed by theregional uplift zones. The large scale uplifs and depressions trend east-west ornortheast. The cross area between the east-west trending and northeast trending upliftzones forms the uplift peak, and the cross area of the two groups of depression zonesforms the depression centers where preserve most of the Mesozoic volcanic-sedimentaryrocks and forms the sedimentary basins.
The space distribution of Mesozoic regional uplift and depression can bediscribed by a function Z(x,y) which is a complicated Futia function of geographicalfactors X and Y: Z=Z(X, Y)=e~1-x/18.5·cos 2π/18.5·X+[1.75-0.75·cos-π/17×(0.66262·X-0.74896·Y)]×cos 2π/17·(0.66262.X-0.74896·Y)
In tie uplift zone, Z(x,y)≥1 and, in the uptift center, Z(x,y)≥2. In the depressionzone Z(x,y)≤0 and in the depression center Z(x,y)≤-1.
3. The genetic types of Mesozoic granites and their distribution
Mesozoic granite intrusion is a very important event of Mesozoic crustal movementwhich formed more than 300 granite intrusive bodies. These granites can be dividedinto four genetic types, S-type, I-type, M'-type and A-type. S-type and I-type granitesoriginated from the crust. M'-type and A-type granites originated from the combinationof part-melted lower crust and upper mantle rocks. The four types of granite aredifferent in mineral composition, C.I.P.M.norminate calculated minerals, petrologicalcharacteristics and geochemistry.
S-type granites mainly formed in late Palaeozoic era-Indosinian stage anddistribute in Chongli-Chende-Fuxin9 ductile shear zone. Phanerozoic I-type granitesformed in every stage in Mesozoic era and distribute along the deep faults in thecrust. M'-type granites mainly formed in Indosinian-Yanshanian stages and A-typegranites mainly formed in late Yanshanian stage. These two lypes of granitedistribute in the latitudinal and Neocathaysian NE-NNE trending deep fault zones whichentered the upper mantle in Mesozoic era.
4. The spatial Distribution of K20 content of Mesozoic granites and its Relationwith Mesozoic palaeo-Moho depth.
Many geologists such as W. R. Dickinson and Mitsushiro Toriumi, etc. noticed therelationship between the K20 content of magma and the distance from the deducted zoneof oceanplate. Though Yanshan area located in the Inner part of continent plate, thespatial distribution of the K20 content in Mesozoic granites is apparentle regular,which is hardly fit the theory of plate tectonics.
Statistic analysis show that the relation betweem the K20 content in Mesozoicgranites and the Mesozoic Moho depth(H) in Yanshan area is as follow:K20(％)=0.374+0.101.H
This kind of linear relationship between K20 and H is also developed in theory asfollow:K20(％)=A+B.H
These formuta can be used to calculate the Palaeo-Moho depth which is aimportant numerical index to analyse the deep structures in geological history.
The Mesozoic pataeo-Moho depth in Yanshan area is determined according to aboveformula and the results are used to discuss the Mesozoic deep structure.
5. The characteristics of Mesozoic fault activity.
Mesozoic fault activity is very strong and very important in the process ofMesozoic tectonic evolution. The Mesozoic faults in Yanshan area include the highangular reverse faults, normal faults, thrust faults, ductile shear zone, circularfault systems, shear faults and synsedimentary faults. The main characteristics ofMesozoic fault activity are as follows:
(1). The spatial accompanionship among Mesozoic deep faults, regional uplift and granites.
(2). The equally space distribution of Mesozoic tectonic zones include the fault zones.
(3). The multiphases of fault activity.
(4). The difference of faults in vertical dimension.
(5). The apparent trending of regional fault deformation from plastic and ductile inlate Palaeozoic-Indosinian stages to brittle in Yanshanian stage.
(6). The close genetic corelation between fault activity and other geological eventsin Mesozoic era.
Ⅲ. The Pataeotectonic Evolution in Different Stages of Mesozoic Era in YanshanArea
The study of palaeostructures is very important in analysing the structureevolution and geodynamics, which was noticed and pointed out by many famous geologistssuch as the former Prof. Li Siguang.
1. The main methods in palaeostructure geology
The main methods in palaeostructure research include: (1).to use the palaeo-temperature meter, palaeo-pressure meter and palaeo-stress meter etc. for analysingthe regional tectonic setting the sedimentary and geographical enviroment, thepalaeostress field, etc., (2). to use palaeomagnetism and strain of tectonic activityfor determing the location and trend of structures and massive bodies, (3). toidentify the ages and kinematic properties of structures and (4). to use geologicaland structure measures for analysing the palaeostructures and their relationships withgeological events.
In recent years, new technology and new methods are widely used in palaeostructuregeology, such as the isotopic dating of structures, the mathematical analysis ofpataeostructures etc.
2. Late Pataeozoic-Indosinian tectonic evolution
In Palaeozoic era-Indosinian stage the latitudinal structure system, the earlyNeocathaysian structure system were dominated in Yanshan area.
The main Palaeozoic-Indosinian latitudinal structures are Kangbao-Weichang faultzone, Chongli-Bamiao-Fuxing tectonic zone, Panjiadian-Xiabangcheng fault zone,Xinglong-Qinglong fault zone and some folds such as Malanyu synanticline, etc. Mostlatitudinal fault zones consist of reverse faults white Chongli-Damiao-Fuxing tectoniczone mainly consists of late Palaeozoic-Indosinian latitudinal ductile shear zones, S-type granites and many tectonic intrused basic-ultrabasic rock distributed in thistectonic zone.
The main Indosinian northeast trending structures which are some composition ofthe early Neocathaysian structure system are Paishanlao-Jinzou ductile shear zone,Jinchangyu-Shangyong ductile shear zone, Bajiazi-camel Mt. reverse fault, Chaoyang-Beipiao reverse fault, etc. and many northeast trending synclines and anticlines.
The skeleton of Malanyuε-type structure system also formed in Indosinian stage.
The regional maximum compressional stress changed from south-north trending inlate Palaeozoic-early Indosinian stage to northwest-southeast trending in lateIndosinian stage. The main deformational enviroment changed from deep crust wheretemperature and pressure were higher to upper crust where temperature and pressurewere much lower.
3. Early ganshanian tectonic evolution
In early Yanshanian stage the main pataeostructure systems are earlyNeocathaysian structure system, latitudinal structure system andε-type structuresystems, Circular structures and northwest trending fault zones also occurred in earlyYanshanian stage.
Most main faults of each structure system in early Yanshanian stage consist ofreverse faults which are compressional-shear while some main fault zones consist ofsynsedimentary faults. In early Yanshanian stage the uplift zones and depression zones werecompositions of the latitudinal structure system and Neocathaysian structure system.The activity of early Neocathaysian structure system,ε-type structure system andnorthwest trending faults reached tomaximum in early Yanshanian stage.
The early Yanshanian faults were ductile-brittle or brittle and most folds wereopen and simple. The skeleton of Mesozoic structures mainly formed in early Yanshanianstage. The deformational enviroment in this stage was the upper crust to crust surfacewhere temperature and pressure were lower. In regional stress field in earlyYanshanian stage the maximum compressional stress treaded northwest-southeast.
4. Late Yanshaniaa tectonic evolution
The tectonic figure in late Yanshanian stage is totally different from those inabove earlier Mesozoic era. The main late Neocathaysian structure system which iscomposed of NNE trending faults and sedimentary basins, formed in late Yanshanianstage. The activities of the early formed structure systems such as the earlyNeocathaysian structure system, latitudinal structure system andε-type structuresystem were weak in late Yanshanian stage.
The deformational enviroment was the crust surface where temperature and pressurewere low and most of the faults were brittle. The regional maximum compressionalstress trended NWW-SEE.
Ⅳ. The Classification of Gotd, Silver and Multimetal Deposits and Their GeologicalCharacteristics in Yanshan Area.
1. The classification of deposits
There are more than 300 gold, silver and mutimetal deposits in Yanshan area, whichcan be divided into 19 types according to the mineralizational genetics and the ore—bearing rocks. The 19 types of deposits are: (1). the magmatic hydrothermal geneticquartz vein type gold deposits (simplified as quartz vein type gold deposits), (2).altered rock type gokd deposits, (3). volcanic rock type gold deposits, (4). du(?)tileshear genetic gold deposits, (5). Palaeoconglomerate type gold deposits, (6).metamorphic hydrothermal genetic gold deposits, (7). porphyry gold deposits, (8).magmatic hydrothermal genetic silver deposits, (9). volcanic rock type silver deposits, (10). skarn copper deposits,(11), marinal volcanic hydrothermal genetic copper deposits, (12). sulfide bearin9 quartz vein type copper deposits, (13). sedimentary strata lead-zinc doposits, (14). skarn lead-zinc deposits, (15). magmatic hydrothermal geneticlead-zinc deposits, (16). metamorphic genetic lead-zinc deposits, (17). skarnmolybdenum deposits, (18). porphyry molybdenum deposits and (19). magmatichydrothermal genetic vein type molybdenum deposits.
2. The geotogical characteristics of the main types of deposits
The 19 types of deposits in Yanshan area have different geologicalmineralizationCharacteristics.
(1) Quartz vein type gold, silver, lead-zinc deposits
Quartz vein type gold deposits are very important in Yanshan area, such as Jinchangyugold deposit, eposit, Yerya gold deposit, etc. The ore bodies are mainly quartz vein inthe compressional-shear faults and shear faults. Near the gold bearing quartz vein therocks altered and the altered rocks are narrow and linear. The hydrothermalmineralization can often be divided into 3-4 phases in which the multi-sulfides phasedeposited most of the gold in the deposit. The quartz vein siver, lead-zinc andmolybdenum deposits have the similar characteristics exclude the metal content andalteration in the ore which are different from the gold ore.
(2). The altered rock type gold deposits
Altered rock type gotd deposits preserved in the widely distributed altered rockswhich is often granitic rocks. The large-middle scale altered rock type gold depositswere found in S-type granites such as Haogao gold deposits in Yanshan area and Jiaojiagold deposit, in northeast Shandong province in China. The gold bearing sulfides oftencontaminated in the wide altered rocks which devoloped along the compressional brittlefaults. The other characteristics are similar to quartz vein type gold deposits.
(3). Ductile shear genetic gold deposits
The ductile shear genetic gold deposits are contaminated in the altered ductileshear mylonites where the gold bearing sulfides preserved such as the Paishanlao large-scale gold deposit. The gold moved away frem the source rocks into the heat waterduring the ductile shearing and deposited in the sulfides when the temperature felldown.
(4). Volcanic rock type gold, silver, copper deposits
This type of deposits were mainly contaminated in early Cretacious basic-acidvolcanic rocks such as Nailinggao gold deposit, Zhaizhang copper deposit and Manhantousilver deposit, etc. Some mineralization was related to lower temperature hydrothermalrock alteration and their ore bodies were often closely controlled by the circular volcanic structure systems. The others wererelated to magmatic hydrothermal activities and controlled by the regional faults.
(5) The skarn copper, lead-zinc and molybdenun deposits
The skarn copper lead-zinc and motybdenum deposits were related to skarnizationof Mesozoic magmatic intrusive rocks such as Suwangfen copper deposit, Bajiazilead-zinc deposit and Beishongsumao molybdenum deposit. The economic metalelements contaminated in the skarn and its related altered rocks or preservedin the sulfides -quartz veins. Copper, lead-zinc and molybdenum skarn mineralizationswere related separately to grandiorites, quartz granites and granites and distributedin different altered zones
(6)The sedimentary strata lead-zinc deposits
The sedimentary strata lead-zinc deposits formed in middle proterozoic riftingstage and was accompanied. by the sedimentation of Carbonate rock strata. The orebodies are mainly stratified and tamellar.
(7)The porphyry gold, copper and motybdenum deposits
The porphyry gold, copper and molybdenum deposits are related to the porphyrygranites and grandiorites in which the main sulfides contaminated inthe planardistributed rocks. Gold, copper and molybdenum mineralization located in differentatterization zones.
The other types of deposits such as the metamorphic hydrothermal genetic gold,copper, lead-zinc deposits, the pataeocongtomerate type gold deposits are notimportant in Yanshan area.
In many deposits, there were more than 2 types of mineralization coexisted inthe same mining field and in some cases transitional mineralization occurred
Ⅴ, The Mineralizational Periods of Gold -Silver -Multimetal in YanshanArea
There are three different views about the regional mineralizational periodsof gold and silver deposits in Yanshan area. Here the dating of morethan sixtyimportant gold, silver, copper, lead -zinc and molybdenum depositsare discussedaccording to different kinds of data.
1. The main methods in mineralizational chronology
Three kinds of methods are used here: (1), the lead isotopic dating of ore,(2),the K-Ar and Rb-Sr isotopic dating of altered minerals. (3).mineralizationaldating from the geological data.
The former lead isotopic models are too simple for the complicated open isotopicsystems. After studing the lead isotopic evolution the author set up a system oflead isotopic evolution modets which are useful in the dating of complicatedgeolgical processes in such area as Yanshan area where geological and tectonicsetting are very special in the Earth surface as discussed before in this article.
The isotopic datings of K-hr and Rb-Sr chronology are also very important instuding the ages of deposits.
In many cases, dating from gelolgical data is also very useful.
2、The main mineralizational periods
The ages of more than sixty deposits are determined by above chronologicalmethods. The results show that there had been four periods of regional mineralizationin Yanshan area, they are Archean-early Proterozoic era, middle proterozoic era, latePalaeozoic era-Indosinian stage and Yanshanian stage. Yanshanian stage is the mostimportant period of regional minerelization. Most large-middle scale deposits of gold,silver, copper, lead-zinc and motybdenum formed finally in Yanshanian stage.
Ⅵ. The Spatial Distribution of Mesozoic Mineratization in Yanshan Area
Regional spatial distribution of mineralization in Yanshan area is analysed bystatistic calculation.
1. The main factors controlling the regional mineralization
In Yanshan area there were three important factors in Mesozoic regionalmineralization. These factors are mineralizational source rocks, magma activity andstructures. The main source rocks are Archean-early Proterozoic metamorphic rockseries. Mesozoic granites and their similar volcanic rocks are apparently related tomost of the formation of deposits. The Mesozoic structures, especially the regionaluplift zones and faults in the centers of the uplifts, controlled the distribution ofthe Mesozoic regional mineralization directly and indirectly. The combination of thesethree factors determined the spatial distribution of gold, silver and multimetaldeposits in Mesozoic era in Yanshan area.
2. Regional spatial distribution of Mesozoic mineralization
Most Mesozoic gold, sitver and multimetal deposits distributed in five northeasttrending mineralizational zones and three latitudinal mineralizational zones. In thecross areas of the two groups of mineralization zones formed the regionalmineralizational centers which distributed in equal spatial separation.
3. The probability model of spatial distribution of Mesozoic deposits
The regionat Mesozoic mineralizational zones and centers are strictly limited bythe regional Mesozoic uplift zones which controlled the spatiat distribution ofregional faults, the mineralizational source rocks and ma9ma activity. Thisrelationship can be analysed numerically by statistic calculation.
The probability of the distribution of Mesozoic deposits, P(x,y), can be described asIn above formula P(x,y) or P(z) is the probability function, Z or Z(x.y) is thefunction to show the location of any deposits in tectonic field, and X, Y represents thegeographic position These formula can be used in regional mineralization prediction
ⅦThe Relationship between Mcsozulc Tectonic Evolution and Regional Gold-Silver-Multimetal Mineralization in Yanshan Area
The relationship between tectonic evolution and regionat mineralization attractedthe attention of many geologists. As a special type of orogenic zone, Yanshan area isrepresentative in studing such relations
1. The limitation of tectonic evolutional phases to regional mineratizationalperiods
In Yanshan area tectonic evolutional phases have apparently limitation to regionalmineralizational periods. Each tectonic evolution phases accompanied a period ofmineralization of gold-silve multimetal deposits. The four important phases, Archean-early Proterozoic era, middle Proterozoic era, late Palaeozoic-Indosinian stage andYanshanian stage, are all important orogenic stages in Yanshan area and all acompaniedby regional mineralizational periods of gold-silver-multimetal. The geological events ineach phase determined the types of deposits in the correspondent periods. From middleProterozoic era to Yanshanian stage the strength of crustal movement increased and thestrength of mineralization increased, too. Both the crustal movement strength andregional mineralizational strength in Yanshanian stage reached to maximum.
2. The limitation of regional structures to mineralizational zones.
In Yanshan area different magnitude of structures controlled different scale ofmineralizational units, the equally spatial distribution of Mesozoic structures lead tothe equally mineralizational spatial distribution.
3 important types of gold deposits in Mesozoic era, quartz vein type gold deposits,altered rock type gold deposits and ductile shear genetic gold deposits distributed in3 different kinematic types of faults: shear-compressional brittle faults,compressional brittle-ductile faults and ductile shear mylonite zones.
The Mesozoic regional stress field also controlled the spatial distribution ofregional gold mineralization in each Mesozoic mineralizational centers such as inQilong mineralizational center. The main gold mineralizational zones trended alang thegraded zones of palaeo-maximum-shear stress in early Yanshanian, stage in Qilong area.
3. The limitation of ore field structures to the spatial distribution of orebodies
Five types of structure system in ore field controlled the spatial distribution oforebodies in Yanshan area. They are (1). circular fault system which limited theorebodies of vein type of gold, lend-zinc and molybdentm and volcanic rock type ofgold-silver deposits,(2)λ-type fault system in plane and in cross section whichcontrolled the orebodies of vein type and bedded-like orebodies,(3).ζ-type faultsystem, (4). ductile shear zone which controlled the ductile shear genetic goldorebodies and (5). rotational fault system which controlled magmatic hydrothermalgenetic ore bodies of gold. In some ore fields more than two types of structuresystem coexisted in the same field to contrall the distribution of orebodies.
4. Regional genetic model of Mesozoic mineralization and the direction for depositprospecting
By considering the factors of regional mineralization and the relationship betweenMesozoic tectonic evolution and regional mineralization, regional genetic model ofMesozoic deposits of gold-silver-multimetal is developed, which mainly show thetectonic setting and spatial position of mineralization in Mesozoic tectonic field.
The prediction of 6 regional mineratizationat centers and their evaluation forprospecting are discussed in detail. The prediction for looking for ductile sheargenetic gold deposits, altered rock type deposits and bed-like vein type of gold-silver deposits is also discussed and evaluated.