| ON THE TECTONO - PETROFACIES FORM AND LINGLONG-JIAOJIA-TYPE GOLD DEPOSITS IN THE JIAODONG PENINSULA, CHINALii GuxianInstitute ofGeomechanics, CAGS, Fahuasi, 100081, Beijing, ChinaIntroductionThe Jiaodong Peninsula is one ot" the most important bases of primary gold resource and mining in China, of which the gold mining history can be traced back to the Tang and Song Dynasties (1007) and the geological study has been extensively and deeply made since the 1930s.The term "Linglong-type gold deposit" is derived from the research paper "Linglong Gold-Copper Deposit in Zhaoyuan County, Shandong Province" by prof. Guo Wenkui (1949) . The 6th Geological Party of Shandong (1977) found another type of gold deposit, named the Jiaojia- type gold deposit. Deposits of the Linglong type (quartz vein type) and Jiaojia type (veinlet-disseminated phyllic rock type) form the main commercial reserves of the study area, and are generally considered to be one type of gold deposits in recent researches.This paper puts forward the term "Linglong-Jiaojia type" (quartz vein-phyllic altered cataclasite type in shear zone) for describing the large gold deposits mentioned above, which are at present of a new gold deposit type in the world (Lu Guxian and Kong Qingehun, 1987) . Based on the theories of geomechanics and tectonodynamic petrogenesis and metallogenesis (Li Siguang, 1929; Yang Kaiq-ing, 1979), the author has studied the distribution of petrofacies and gold ore controlled by structrues of different orders involved in this type of deposits, discussed further the characteristics of sturctural control over generation of the petrofaeies and deposits, and emphatically analysed the physieoehemical genesis of these processes on the basis of "the ef- fect of tectonodynamics on hydrostatic pressure".Aâ… .Tectono-petrofacies Form in the Jiaodong PeninsulaOn the basis of deformation, the author has classified the structural features and de-fined structural zones and domains with varying deformation intensities, i.e. the compressive, shear and tensile zones and domains. This involves the establishment of an-other concept the tectono-petrofacies form, which means a combination of structural zones and domains with a certain distribution and a genetic relation to geologic and tectonic processs, including sedimentary, igneous, and metamorphic facies affected by tectonics as well as physicochemical conditions and geologic environment reflecting their formation and development.This paper formally puts forward that there are dense ENE regional linear structures in the study area and assigns the NE compresso-shear sturetures in the west part of the area to the Cathaysian, through field geologic work and compilation of 1:200, 000 tectono-petrofacies maps. On such a basis, the paper defines a reversed "S" shape or fiat-lying "～" shape for the arcuate fault-fold metamorphic petrofacies form extending in the E-W direction in the pro-Mesozoic (?) basement and a reversed "(?)" shape for the tectono-petrofacies form in thc Mesozoic.The latter is regard as the structure controlling the mineralization of gold.â…¡.Ore Source Series (Sequence) of Linglong-Jiaojia-type Gold DepositsWhat is the gold source? The Jiaodong Group, the mantle, the Guojialing dioritic granite, or the Luanjiahe granite7 These opinions, which have their respective geologic evidences, are still controversial. The author has established an evolution series of source rocks which is deseribed as follows: as their carrier rocks were formed, changed and de-formed, the mineralizing materials were discontinuously dispersed, transported and redistributed and finally produced a deposit; this process plus the rock associations re-flecting the process constitutes the evolution series. In the light of the temporal and spatial relations of the rock associations with the mineralizatoin, we classify thc Precambrian metamorphic rocks as the intermediate source series whose original submarine intermediate-basic volcanics and elastics are the initial ore source series, and the granites formed by metasomatism and remelting of them are the direct ore source rocks.An extensive study of geological characteristics of consanguineous evolution of source sequences has been made. A lot of evidence has been obtained from isotopic and other re-searches: 1) The Jiaodong Group is consistent in common lead composition with the de-posits: theirμvalues are respectively 9:31 and 9.24, Th/U values 4.02 and 4.17, and their model-lead ages are alike, too, showing that they were derived from the samc mother rock; 2) the averages ofδ34S of the Jiaodong Group, the granites and the depos-its are all positively deviated from that of meteoritic sulfur, being 7.4ï¼…, 9.5％。and 9.1ï¼…, respectively; 3) the initial whole-rock (87)Sr/(86)Sr ratios of the three kinds of granites and that of the single mineral of deposits are similar, i.e. 0.718, 0.714, 0.709 md 0.7116, respectively, suggesting that they are products of the same geological pro-cess of crust source; 4)δ(18) O ofquartz from the three kinds of granites are 9.0ï¼…, 10.4％。and 8.34%, and that of hydrothermal fluids of quartz of gold ore is 9.18ï¼…, andδD is smaller, falling in the magmatic field when plotted on a diagram.Besides remarkable geological characterstics, there are other evidence for distin-guishing ore source series or sequences; 1) difference exists in age; 2) the lead isotope of deposits is distributed along the (204)pb errorchron, but that of the Jiaodong Group and its quartz veins forms a secondary isochron, reflecting the difference in direct source, al-though the lead evolution curves of both of them intersects the single-stage lead curve at 850 Ma; 3)δ(34)S of deposits is close to that of direct source rocks but quite different from that of intermediate ore source rocks; 4) the gold content of intermediate ore source rock is higher (19.1 ppb), and that ofthd direct rock lower (4.25 ppb), but the gold contents of the latter's hydrothcrmally altered veins (9.76ppb) and derivative dike rock (66.3 ppb) are high; 5) the REE pattern shows that the ore source rocks had evolvedtoward a higher degree ofmagmatization and have a high enrichment in La, Ce, Pr and Nd that reflects a strong and wide alteration of K and Na.â…¢.Attributes of Tectono-magmatic FaciesIn previous studies, granitcs were distinguished mainly by remelting degree, protolith and content of mantle material, ctc.. The author has made study of this problem in terms of different attributes of tectono-magmatic petrofacies.The Linglong-type gneissoid biotite granite has the c-s fabric (α≈30°±), showing a superposition of shearing on compression; the Guojialing-type porphyritic dioritic granite possesses the c-s fabric (α≈0°±), suggesting a stationary compression; the LuanJiahe-typc equigranular granite is charaeterised mainly by intrusion, with the rock bodies showing a tensile deformation and a non-oriented fabric. A geotectonic researcb in-dicates that the characteristics of development (＞164 Ma±→134 Ma±→124Ma±) from shear, compessive to tensile structural petrofacies are suitable to the environment of the Indosinian and Yanshanian movements in eastern China.From the comprcsso-shear structural Linglong-type granite, the compressive struc-tural Guojialing-type granite to the tensile Luanjiahe-type granite, the petrochemical composition changes from a moderate to low to high acidity; the marie composition from being moderate to high to low; the distance from the eutectic area and trough for projec-tion points in the Q-Or-Ab and An-Ab-Or triangle diagram varies from moderate to great to small; the DI and PL frequency diagrams show that the tensile facies have a bimodal distribution in the intermediate-basic area, and the DI and PL peak values of three kinds of granites are 80～90→73～82→85～93 and 7～17→13～23→5～10 respectively and in proper order; in the AFM diagram, the points are concentrated to-wards the top of alkali at a low angle to the AF line, then almost perpendicular to the FM line as a whole, and then parallel to the AF line with a few points being dispersed near the FM line; with increase of SiO2, the CaO / Na2O＋K2O ratio decreases slightly in two di-rections, then decreases little or is almost unchanged, and then sharply decreases. The compressional and tensional petrofacies are comparable with the study results of over 1300 samples from the coasts ofthe Pacific and Atlantic (Petro, W.L., 1979), and the shear petrofacies can be used for explaining and supplementing the data previously considered to be a reflection between the above two petrofacies.V.Linglong-Jiaojia-type Gold DepositsThese gold deposits are the pyrite quartz vein-phyllie altered cataclasite type occurring in shear zone of granite of the Mesozoic. Material base of alteration-remelting of the granites comes from a Precambrian sedimentary-metamorphic series containing interme-diate-basic volcanics. Because of different properties of ore-controlling structurs, these deposits can be assigned to two forms or types of mineralization; the Linglong quartz vein and the jiaojia altered rock, which are closely associated with each other and have similar and evenly distributed isotopic compositions of Pb, S, O, C, etc., an indication that they are postmagmatic hydrothermal deposits with the same genesis.V.Zoning of DepositsIt was generally considered that there is a vertical zoning for single ore body, with the quartz vein being in the upper part and the phyllic rock in the lower. Research shows that in the Linglong ore field, the three sets of structural mineralization zones arc all characterised by a horizontal zoning with a gradual change from phyllic alteration ore body in the main comprcsso-shear zone to quartz vein in the tcnso-shear zone of the foot wall. In measuring geloical sections, we have discovered that the phyllic foliation has a conju-gate relation with gold quartz veins, but is opposite in dip to them, when using a set of stable phyllic structural foliations with the same dip as the main compresso-shear zone. Drilling and excavation show that the shallower part is a phyllic ore body with the same SE.dip as the main comprcsso-shear zone, but the lower part becomes a quartz-vein ore body dipping northwest. In the Jiaojia gold deposit, a set of quartz flow cleavages parallel to the main structure is in a conjugate relation to a swarm of quartz-sulfide veins. These features, coupled with the characteristics of the wide alteration and mineralization zoning in this region, make it reasonable to believe that the early mineralized altered phyllic rock associated with primary conjugated shear faults was later converted into supcrposed phyllic ore body in compresso-shear zone and into metasomatic-infiUing ore quartz vein in tensso-shcar zone.The crystal characters of pyrite of thc q uartz-vein and phyllic ore bodics change in the same way downward :ï½›100ï½â†’ï½›100ï½â†’ï½›111ï½â†’ï½›210ï½â†’ï½›100ï½â†’ï½›210ï½; the el-emcnt associations of them also vary similarly: For thc phyllic orc, Sb, Ag, Au, Se, Bi→(AS), Ba, Mo→Zn, Mn, Co, Ni, and for the quartz vein, Ag, As, Au, Co, Bi→(Sb), Cu, Ni, Mo→Zn, Mn, W. The two types of orcbodics are parallelly developed, without vertical connection.â…£. Structural and Tectono-dynamic ControlsIn section, the phyllic orcbody of main compresso-shear zone and the quartz vein of tensso-shear zone with an opposite dip in the foot wall form a lambda-typc pattern, but in plan, they extend parallelly. The phyUic orebodies arc thicker and larger, with a lower but stable tenor (5.13g/t), of which the gold mineral contains 63～70% Au and the ore is low in sulfur (3～4%); the quartz vein bodies are Smaller and greatly varied, with a tenor of 10～25g/t, of which the gold mineral has 50～60% Au (generally Ag＞Au) and the ore is high in sulfur (8～20% ) .In addition,δ34S values of the quartz veins are lower, averaging 7‰, but those of altered rock are higher, averaging 9.22‰. In the sec-tion of the Potouqing NE ore zone, the purity of gold changes from 898.9, 958.7, 761.2 to 454.4 from the center of the zone to the foot wall; orebodies of structural zones are somewhat different in REE distribution, with LREE being concentrated in tenile zone and HREE in compresso-shear zone, Alteration characteristics are not the same: during alteration, Si, K, OH and Fe increased but Na and Al decreased in phyllic altered ore zone, whereas K, Fe, OH and Mg increased but Si and Na reduced in quartz vein zone. In short, these regular changes reflecting the diffferences of physicochemical condi-tions suggest that the differences in macroscopic mineralization type, geochemical anoma-ly and location of industrial orebodies are caused by the effect and control of tectono-dy. namies. Pts=-0.182＋0.142α＋0.441x＋0.337αx-0.02α2where x is the latitudinal evenly distributed force; assuming y is the longitudinalforce, we need only to defineα=Y/X.3.The additional hydrostatic pressure is regarded not only as the physical variablc, causing the change of rock volume but also as a physicochemical parameter affecting chem-ical process.â…¡.Depth-Measuring Method with Tectoinie correctionThe depth was traditionally estimated by the pressure value derived from inclusion or mineral ,measurement. The pressure measurements of the vertical and horizontal systems at Xishan, Linglong, show that the vertical pressure gradient is up to 120b±/100m, but the total pressure gradient of rock load and fluid pressure is less than 50b±/100m. This suggests that some other pressure source should be considered. The horizontal pres-sure gradient is up to 50b±/100 m in the area.We may measure the strain and ancient stress (using mineral dislocation-density method) in rock samples and suppose that the ratio between plastic strain and general strain is a constant.(?)is a constant,(?)by means of the equations:we may get the values of 3 principal stresses, which are the values of stresses causing residual (plastic) deformation.Based on this, we may obtain the structurally added hydrostatic presssure.The measurement of orebodyâ… at 70 m beiow surface in the Jiaojia gold deposit indi-cates that the metallogenetic depth of the orebody is-918.59m±(on the basis of 1300 atm) or-543m±(on the basis, of 1200 atm), quite different from the depth of 3～4km estimated by previous scientists.â…¢.Physicochemieal State of Petrogenesis and Metallogenesis in Tectono-Mineralization ZoneMeasurement and calculation of the composition of mineralization fluid and relevant parameters have resulted the following;1 .Variation of contents of constituentsThe mineralization fluid constituents at high-and low-temperature stages in different structural zones vary similarly, i.e.with high contents of K+, Na+, CI-, SO44, CO2and H2O and low contents of Ca++, Mg++ and CO in tensile zone. However, the content ranges of high-and low-temperature constituents differ greatlly: ratio values of K+,Na+, SO44 and CO of fluid of different structural zones at high-temperature stage are 0.837, 0.51, 0.248 and 0.994 repectively, but the tatio values at low-temperature stage are 1.44, 0.247, 0.076 and 4.54 rcspectively. This shows that the large-scale migration and dispersion of fluid constituents took place at the high-temperature stage, but the great change in contents of the constituents that affected the mineralization took plaee mainly in the medium-to low-temperature stage.2.Changes of activities of the constituentsThe ratios of activities of K+in three sections of the Linglong gold field are 1.845 (1.002 at higher temperature), 15.41 and 21.26, while those of Na+are 0.669, (0.655 at higher temperature), 0.40 and 0.965. It is thus clear that the change of alkali closely re-lated with gold metallogenesis was caused mainly by the distinct variation of K+ activity in different strucural zone.3.Variation of physicochemical parametersThe reducing index is high in compression zone, and low in tension zone. For in-stance, the reducing indexes of the NNE zone in the Linglong gold ficld are 0.166 and 0.026 respectively in compression and tension zones, and those of the NE zone are 0.55 and 0.013. The pH valus of altered rocks in compression zone are low, e.g. they are 5.7047 and 6.3778 in two structurd places in the NNE zone and 5.8599 and 7.8427 in two places in the ENE zone. The fugacity of sulfur in compressive zone is high, whereas the fugacity of oxygen in tensile zone is high.â…£.Order and Direction of the Development of Tectono-petrofacies ZoneUnder other identical or similar conditions, a tensile domain (zone) and compressive domain (zone), as a whole relatively closed system, may develop freely, in which the chemical reaction and evolution proceed always in the dircction of the genera. tion of rock and mineral of tensile area. This can be proved by the following:If P1 and P2 reprcsent two local pressure states,where(?)If P2＞P1,â–³G＞O, Thus the process will not proceed spontaneously in nature.If P2＜P1,â–³G＜O, Thus the process can proceed spontaneously in nature, and develop from P1 state to P2 state.Câ… .Shear solutionThe following is the recognition and study of shear solution. The grey quartz in quartz vein of tensile zone exhibits a euhedral-subhedral equigranular texture, and is arranged along the "X" conjugate shear trend to make up an oriented structure. The'existence of such an arrangement has been further verified by X-ray fabric study of quartz {1010}. The texture and structure, which are considered to be a "shear solution', can not be ex-plained by the "pressure solution" theory. This shear sloution marks a kind of mechanism of deformation and petrofaeies change, by which the rock and mineral acted upon by force are characterised mainly by solution on conjugated shear plane and by precipitation and crystallization in vertical shearing direction (Lu Guxian, 1982).â…¡.The classification of Compresso-sbear zoneThe main compresso-shear zones in the study area can be divided into threesubtypes: the poly-track, po]y-directional; the single-track, double-directional; and the single-track, single-directional. They ruoghly have their respective corre- sponding zones of tectonites, i.e. the beaded braccia-shattered mylonite zone, the rod-like braccia-shattered mylonite-mylonite zone and the schistose (lenticular) braccia-mylonite zone. This classification provides new indicators for identifying the mode of tectonism and the formational process of structures, and is thus helpful to the study of shear zone in the future.â…¢.The pattern of the en echelon structuresThe en echelon veins and faults in the study area are grouped into four patterns: the left oblique-left dipping, the left oblique-right dipping, the right oblique-left dipping and the right oblique-right dipping. The classification is of practical significance in mining and exploration of mineral deposits.The author is grateful to Prof. Yang kaiqing for his direct guidance in preparation of this DSC dissertation.
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