1. Introduction

The Northeast Jiangxi Deep Fault is an importantboundary fault in eastern China, representing a suture linebetween the Jiuling Terrane in the west and the Huaiyu-shan Terrane in the east. As shown in Figure 1, strikingnortheastwards, its southern end starts from Dongxiangcounty town near Nanchang city, via Dexing andWuyuan in northeastern part of Jiangxi province, andvia Shexian and Ningguo in the eastern margin of Anhuiprovince, and merges in the Taihu lake area at the south-

Tectono-Magmatic Evolution and Metallogenesisalong the Northeast Jiangxi Deep Fault, China

Ying Ye*, Hidehiko Shimazaki**, Masaaki Shimizu*** and Shouxi Hu****

Abstract : From the southernmost part of Jiangsu province to the northeastern part of Jiangxi province, China, the NortheastJiangxi Deep Fault runs for about 400 km length with a width of 30 to 40 km. This fault marks the suture zone of two ter-ranes of Proterozoic age. At the both sides of the fault, Yanshanian granitic activity is recognized. That is, the Dexing-Wuyuan porphyry belt on the NW side of the fault, and the Damaoshan-Lingshan granite belt on the SE side. The formeractivity is characterized by the occurrence of small stocks of granodioritic composition, rich in siderophile elements but poorin LIL elements. No distinct Eu anomaly is recognized in the REE pattern, and a low initial 87Sr/86Sr ratio is reported. Mag-netite, sphene and apatite are observed as accessory minerals. On the contrary, granitic activity on the SE side of the fault ischaracterized by the occurrence of composite batholiths, in general of granitic to monzogranitic composition, rich in LIL andalkali elements but poor in siderophile and alkali earth elements. A strong Eu anamaly is recognized in the REE pattern, andinitial 87Sr/86Sr ratios are as high as 0.716. Fluorite, zircon and REE minerals are observed as accessory minerals. Thesetwo contrasting granitic activities are refered to as syntexis- and transformation-types, respectively, following the classifica-tion commonly used in China, and have similar petrochemical characteristics to those defined for the magnetite- andilmenite-series, and I- and S-type granitoids.

Considering that the above igneous activity occurred far from the supposed subduction zone along the East Coast ofChina, intracontinental A-type (continent to continent) subduction is proposed to have occurred northwestwards along theNE Jiangxi Deep Fault during Yanshanian time due to a strong compressional stress from SE to NW. A-type subductionintroduced the continental slab to some depth, and resulted in the production of the paired granitic activity observed on bothsides of the fault. Many mineral deposits are associated with both granitic belts. In the Dexing-Wuyuan porphyry belt, theDexing porphyry Cu and Yinshan polymetallic deposits are representative, whereas in the Damaoshan-Lingshan granite belt,several tens of rare metal deposits are known such as the Geyuan Nb-Ta-W-Sn deposits. Metal assemblages of thosedeposits reflect the source materials of magmas in both granitic belts.

Received on September 20, 1997, accepted on February3, 1998

* Dept. of Earth Sci., Zhejiang University, Hangzhou,China, 310027

** Geological Institute, University of Tokyo, Hongo 7-3-1,Tokyo 113-0033, Japan

*** University Museum, University of Tokyo, Hongo 7-3-1,Tokyo 113-0033, Japan

**** Dept. of Earth Sci., Nanjing University, Nanjing, China,210008

Keywords: NE Jiangxi Deep Fault, A-type subduction, Syn-texis-type granitoid, Transformation-type granitoid,Dexing porphyry Cu deposits, Yinshan polymetallicdeposits, Geyuan Nb-Ta-W-Sn deposits.

RESOURCE GEOLOGY, vol. 48, no. 1, 43–50, 1998

Fig. 1 Index map. Dashed line shows the approximateposition of the NE Jiangxi Deep Fault.

43

ernmost part of Jiangsu province, stretching about 400km long and 30 to 40 km wide.

Igneous rocks with different ages and metallic depositswith different metal assemblages are distributed alongthis fault, for example, the Dexing porphyry Cu deposits,the Yinshan polymetallic deposits and a lot of Au andrare metal deposits, which have received attention notonly because of their economic value, but also of theirunusual tectonic setting.

In 1995 and 1996, the authors carried out geologicalsurvey of several mining areas in the northeastern partof Jiangxi province as part of an international cooperativeproject organized by the relevant universities. Thispaper is a summary of the project, and demonstrates thatthe A-type (continent to continent) subduction model isapplicable, and can explain the distribution and natureof the Yanshanian igneous activity and associated min-eral deposits in the region.

The A-type subduction is defined as that a lithosphericmantle becomes detached from the overlying crust and issubducted underneath the continental crust, by Weber(1981) and Weber and Behr (1983). The A-type sub-duction contrasts with the subduction occurring along theBenioff zone in the Circum-Pacific area (ocean to conti-nent), which is called the B-type subduction. In China, theeastern Qinling orogenic belt is referred as a typical A-type subduction zone (Jia et al., 1988; Hu and Hu, 1990).

2. Tectonic Setting

The volcano-sedimentary formation that recorded theearly history of the NE Jiangxi Deep Fault is represent-ed by the Upper-Proterozoic Dengshan Formation. Itslithological assemblage is described in Table 1.

There is a certain evolution tendency with regards tothe petrologic character of the Dengshan Formation.Volcaniclastic and flysch greywacke increase towardsthe lower part of the formation as turbidites through rel-atively rapid sedimentation, commonly found beyondactive continent margins and island arcs. The volcanicrocks, dominated by basalt and spilite, indicate that thetectonic setting at that time was most probably a subma-rine incipient island arc. Upward flysch formation gaveway to neritic and littoral sediments, with vesicular andamygdaloidal structures becoming common in the erup-tives. The upper part of Dengshan Formation is domi-nated by intermediate to felsic volcanic rocks of conti-nental facies, indicating that the island arc evolved intoits mature stage.

Similar volcano-sedimentary sequences occur in theZhejiang and Anhui provinces and are refered to as theShuangxiwu Formation and Jingtan Group, respectively.Lan and Ye (1991) confirmed their time correlation withthe Dengshan Formation, and pointed out that they were

all formed in an island arc setting based on geochemicalevidence. Numerous ultra-mafic rocks occur along theNE Jiangxi Deep Fault (Fig. 2). Some were once regardedas Yanshanian intrusives. Xu and Qiao (1989) reporteda 929.3±33.8 Ma Sm-Nd isochron age for one of theultra-mafic blocks in NE Jiangxi, and emphasized thatthey are component members of Upper Proterozoicmelange. Zhou et al. (1989) also reported a Sm-Ndisochron age of 1024 ± 30 Ma for the ophiolite sequenceexposed in South Anhui, and pointed out that the ophio-lite is relict sea floor from a Proterozoic marginal basin.

During the Mesozoic, tectonic boundaries in EastChina remobilized because of interaction between theEurasia and Pacific plates. Mesozoic magmatism andmetallogenesis are all controlled by pre-existing region-al faults. For this reason, and also because the inlandarea of East China is so far away from a proposedtrench system in the western Pacific, e.g. more than 800km with respect to the Dexing porphyry Cu mine, Hu etal. (1992) favored to explain the Mesozoic magmatismand metallogenesis in East China by means of intra-con-tinental A-type (continent to continent) subduction.

The presence of A-type subduction along the NEJiangxi Deep Fault is supported by geophysical and geo-logical evidence. Artificial earthquake profiles showthat the present fault plane dipping northwestwards(Zhu et al., 1982), cutting the Conrad and Moho discon-tinuities. Aeromagnetic and gravitational fields on eachside of the fault are also distinctly different. Near thefault, strata of different age, including lower Jurassicrocks, suffered intense dynamic metamorphism.

3. Paired Granite Belts along the NE JiangxiDeep Fault

In the area of study, paired Yanshanian granite beltsare recognized on both sides of the NE Jiangxi DeepFault, that is, the Dexing-Wuyuan porphyry belt on itsNW side, and the Damaoshan-Lingshan granite belt onthe SE side (Fig. 2). Hua and Dong (1982) and Zhu etal. (1982) investigated some of the granitic bodies dis-

44 RESOURCE GEOLOGY : Y. Ye, H. Shimazaki, M. Shimizu and S. X. Hu

Table 1 Lithological assemblage of the Upper-Protero-zoic Dengshan Formation (after Ma et al., 1992).

Yejia Group 1270 mAndesite, dacite, dacitic ignimbrite, rhyolite and rhyolitic tuff, intercalated with basalt.

------ Conformity ------

Bazhukeng Group 1775 mUpper: Tuffite, tuffaceous slate and spilite-keratophyre.Middle: Volcaniclastic gravel-sandstone, tuffite and slate

with graded bedding, intercalated with spilite-ker-atophyre.

Lower: Graded volcaniclastic greywacke, silty slate, intercalated with basalt and spilite.

tributed in these two belts, Shen and Liu (1987) studiedtheir REE geochemical characteristics, while Hu and Hu(1993) emphasized the major differences between thetwo. These workers revealed the remarkably contrastingnature between the granitic rocks of the two belts as sum-marized below, and concluded that the Dexing-Wuyuanbelt belongs to the so-called syntexis type and theDamaoshan-Lingshan belt to the transformation type, fol-lowing the classification of granitic rocks commonly usedin China (e.g. Xu et al., 1980, 1982). According to thesereferences, primary magma of the former is supposed tobe a mixture of mantle derived melt with crustal materials,while that of the latter to be originated from sediments ormeta-sediments via migmatization and granitization.

Intrusives in the former Dexing-Wuyuan porphyrybelt are dominately granodiorite, associated with inter-mediate to felsic volcanic and sub-volcanic rocks, usual-ly occurring as small stocks with less than 1 km2 expo-sure. Porphyries have hexagonal bipyramid β-quartzphenocryst, hornblende and Mg-rich biotite as majormafic minerals and anorthoclase as K-feldspar. Themineral compositions indicate a relatively high tempera-ture and high rate of crystallization of the magma. Con-tents of accessory minerals are generally more than 1volume %, and magnetite, sphene and apatite areobserved. The porphyries are rich in siderophile ele-ments, but poor in LIL elements. No distinct Eu anomalyis observed in their REE distribution patterns. The initial87Sr/86Sr ratio of the Tongchang porphyry, one of thetypical stocks in this porphyry belt (Fig. 3), is 0.7043.

These features indicate the magma originated from thelower crust or upper mantle, without significant differ-entiation through fractional crystallization.

On the contrary, in the latter Damaoshan-Lingshangranite belt, both Damaoshan and Lingshan compositebatholiths occur with exposures over 100 km2. Some smallstocks are also present in this belt. The majority of theseintrusives are granite and monzogranite. Hornblende isscarcely found and Fe-rich biotite is usually the solemafic mineral. K-feldspar is microcline with high tri-clinicity. These data indicate a high fluid pressure andrelatively low temperature during crystallization. Acces-sory minerals are dominated by fluorite, zircon andREE-bearing minerals. Geochemically the granites arerich in LIL and alkali elements, but poor in siderophileand alkali earth elements. Their REE distribution pat-terns are characterized by intense Eu depletion. The ini-tial 87Sr/86Sr ratio for the Damaoshan granite is 0.7163,indicating that the source material of the transformationgranites in this area is mainly sedimentary rocks of theupper crust. High fluid pressure required for the forma-tion of microcline indicates the involvement of an aque-ous phase in the formation process of granite magma.Enrichment of alkali and LIL elements and depletion ofCa, Sr and Eu suggest that the fluid is most probablyoriginated from a katametamorphic zone, where the for-mer elements are mobile but the latter elements tend tostay in relict phases.

The syntexis porphyry and transformation graniticrocks in the NE Jiangxi province are almost comparable

vol. 48, no.1, 1998 45The Northeast Jiangxi Deep Fault, China

Fig. 2 Simplified geological map of the Northeast Jiangxi Province.

from a petrochemical viewpoint to the magnetite- andilmenite-series granitic rocks proposed by Ishihara(1977), and to the I- and S-type granitic rocks of Chappelland White (1974). Although, as is discussed by Takahashiet al. (1980), the latter two rock classifications are notcompletely comparable. In particular, the tectonic envi-ronment of I- and S-type granitic intrusion is signifi-cantly different to those of the magnetite- and ilmenite-series classification originally based on granitic rocks ofthe Japanese island arc system. As stated above, graniticrocks occurring along the NE Jiangxi Deep Fault arebelieved to occur in an inland area along a Proterozoicsuture line due to compressional A-type subduction duringMesozoic time. The occurrence of similar paired granitebelts is also recognized by Hu et al. (1990) in the north-ern part of East Qinling, central China, in an almost iden-tical tectonic environment to the NE Jiangxi province.

4. Metallogenic Features of the Syntexis Por-phyry Belt

4. 1 General characteristics

Important deposits have been found in the syntexisporphyry belt along the NE Jiangxi Deep Fault. Amongthem the Dexing Cu deposits and the Yinshan polymetal-lic deposits are well known. The Dexing Cu deposits arerelated to a group of porphyritic stocks linearly arrangedin a NW direction (Fig. 3). The mineralized intrusives arecalled the Fujiawu, Tongchang and Zhushahong stocksfrom ESE to WNW. There are also several other volcanicand sub-volcanic rocks exposed along this trend. The lin-ear arrangement shows that the emplacement of theserocks is controlled by a local fault developed as a trans-verse tensional rupture associated with the NE JiangxiDeep Fault (Zhu et al., 1982). Among the Yinshandeposits, a tensional rupture with NW trend is also recog-nized based on geophysical evidence (Yang et al., 1996).

Alteration zonation in the Dexing Cu deposits is similarto that of typical porphyry Cu deposits in active conti-nental margin and island arc regions (e.g. Rose and Burt,1979). From the intrusion outward, hydrothermal alter-ation zones are recognized as follows: chlorite-sericite-K-feldspar, quartz-sericite and chlorite-(epidote)-illite-carbonate zones. The first zone is developed only withinthe porphyries. Pyrite, chalcopyrite and molybdenite areconcentrated in the altered porphyries and wall rocksnear the contact zone, composing huge orebodies withdisseminated, veinlet-disseminated and veinlet structures.

Located beside the Xishan crater, the Yinshan poly-metallic deposits are related to dacitic porphyries asshown in Figure 4. The upper parts of the deposits aredominated by a Pb-Zn-Ag orebody occurring as singleveins or clusters of parallel veins. Vein mineralizationincludes galena, sphalerite, native silver and acanthitewith minor amounts of pyrite, chalcopyrite, hessite andpyrargyrite. Carbonate, quartz and chlorite are the maingangue minerals. In the middle and lower parts of thedeposits, Pb-Zn-Ag ore gives way to Cu-Pb-Zn and Cu-Au ores, while veinlet and veinlet-disseminated struc-tures become dominant.

The mineral composition in these parts is complicatedwith more than twenty mineral species. Besides Cu, Pb,Zn and Ag sulfides, there are native gold, native silver,electrum, Au and Ag telluride, Bi and W minerals. Thenumber and abundance of sulfide species decrease down-wards. Pyrite and chalcopyrite associated with nativegold predominate at deeper levels. In brief, the upperparts of the Yinshan deposits can be regarded as hydro-thermal Pb-Zn-Ag deposits associated with volcanic tosubvolcanic systems, which transgress into Cu-Au por-

46 RESOURCE GEOLOGY : Y. Ye, H. Shimazaki, M. Shimizu and S. X. Hu

Fig. 3 Geological sketch map of the Dexing Cu mine. Pt2 represents middle Proterozoic strata, and Pt3 upperProterozoic strata. Broken line between them repre-sents the NE Jiangxi Deep Fault.

Fig. 4 Geological sketch map of the Yinshan polymetal-lic mine. Pt2 represents middle Proterozoic strata,dashed line regional fault, and dotted line mineraliza-tion zoning.

phyry deposits at depth. Exploration for deeper exten-sions of the orebodies is actively being carried out, andthe Yinshan mine may surpass the Dexing Cu mine infuture, not only in scale but also in economic importance.

4. 2 Lateral distribution and zonation of ores

In the Tongchang deposit, the main deposit of theDexing mine, Zhu et al. (1982) demonstrated that thelargest thickness of ore-bearing cracks is attained on theSE side of the porphyry, that is, near the NE JiangxiDeep Fault. Mineralization is also relatively concentrat-ed in that area. Thus the major openpit of the Dexing Cumine is located in the southern part of the Tongchangporphyry stock. Based on the geology of more than onehundred hydrothermal deposits in East China, Hu et al.(1992) pointed out that the main orebody of each exam-ined deposit is found generally on one side of the relatedintrusion, that is, on the side nearest to a regional deepfault. They named this phenomenon “lateral distribu-tion”. This pattern indicates that the thrust plane of thedown-going slab and its derived fault system could bethe main fluid path and the structure hosting the ore.

The principle of “lateral distribution” is more appar-ent in the Yinshan mine. The magmatic center in thisarea seems to be the Xishan crater. Almost all productiveorebodies occur in the eastern area of the crater, near to aregional fault parallel to the NE Jiangxi A-type subduc-tion zone. In the western area of the crater, no importantmineralization has been found. Moving away from theXishan crater towards the regional fault, exploited min-eralization is zoned in the sequence Cu-Au, Cu-Pb-Zn,Pb-Zn-Ag to Pb-Ag (Fig. 4).

4. 3 Assemblage of metallic elements

In the Dexing Cu mine, Au and Mo(Re) are importantindustrial elements besides Cu. Average contents of

these metals are reported as Cu 0.73%, Mo 0.017%, Re0.40ppm and Au 0.04 to 1.4 g/t (Zhu et al., 1982). Themetallic assemblage of Cu-Au-Mo(Re) is characteristic,and scarcely found in other porphyry deposits in theworld. In the Circum-Pacific region, some porphyrydeposits of the western United States are rich in Mo butnot Au. In the island arc areas of the southwesternPacific, most porphyry Cu deposits are relatively rich inAu, but in general Mo is negligible. These facts mayindicate that the Au and Mo in porphyry deposits arederived from different sources, that is, the former isbelieved to originate from the subducting ocean floor,while the latter may be related to contamination of pri-mary magma by sialic continental crust.

Such genetical models are applicable to explain theassociation of Au and Mo in the Dexing Cu mine. Withregards to the source of Au, it must be different fromthose deposits of the island arcs because the Dexingdeposits are so far away from the western Pacific sub-duction zone. Ma et al. (1992) reported that Proterozoicstrata in NE Jiangxi are rich in Au with an average con-tent of 28 ppb, seven times higher than the mean Aucontent of the upper crust (4 ppb). Partial melting of theAu-rich basement during A-type subduction is the mostprobable source of Au in the Dexing Cu deposits.

With regards to the origin of the Yinshan polymetal-lic deposits, useful trace element data for the volcanicrocks in the mining area are given by Yang et al. (1996),and can be divided into three groups based on their rela-tive abundance as follows:

a) The first ten elements from Bi to S as shown inFigure 5. This group of elements have relatively highconcentrations in the volcanic rocks of this area. Amongthem, Cu, Pb, Zn, Ag and Au are exploited from theYinshan mine, while Bi and Sb occur in recoverable con-centrations.

vol. 48, no. 1, 1998 47

Fig. 5 Trace element distributionpattern of the Yinshan volcanicrocks, normalized to mean fel-sic rocks (Data from Yang etal., 1996). Diamonds and starsrepresent volcanic rocks of dif-ferent stages, triangles dacite,and crosses subvolcanic rocks.Solid circles are the average ofall rock types.

The Northeast Jiangxi Deep Fault, China

b) The next four elements from V to Sn as shown inFigure 5. Their average abundances are several timeshigher than the mean of felsic igneous rocks, but theseelements are not concentrated to such an extent that theyare exploitable. In the orebodies, ferberite, hubnerite,stannoidite and mawsonite are reported as accessoryminerals.

c) The last eleven elements as shown in Figure 5.The concentrations of these elements in the volcanicrocks of this area are similar to those of the mean of fel-sic igneous rocks, and are not reported to be concentrat-ed in the deposits except for Mo, which is slightlyenriched in the deeper part of the dacite porphyry.

Among the enriched elements in the Yinshan deposits,Au has probably been derived from the basement as dis-cussed above, W and Sn are typical lithophile elements,and Bi and Sb are also enriched in some continentalcrust. The metallic element assemblage of the Yinshandeposits is similar to that of the Dexing Cu deposits,both reflecting the effects of contamination by sialiccontinental crust. This is probably a common featureamong magmatic hydrothermal deposits related to A-type subduction.

5. Metallogenic Features of the TransformationGranite Belt

In NE Jiangxi, several tens of rare metal depositshave been found around the Lingshan compositebatholith, all of them related to the late stage activity ofthe granitic magma. The Geyuan Nb-Ta-W-Sn depositscan be taken as an example. The deposits are foundbeyond the west margin of the batholith (Fig. 2), andlocated on the top of a buried stock and in epi-metamor-phic rocks above the contact (Fig. 6). In the lower part ofthe stock, there is fresh granite which becomes intenselyaltered upwards, from K-Na-feldspathization to greis-enization. Pegmatoid and microcline rims are found inprotruding parts of the granite as shown in Figure 6,which were possibly formed by fluid accumulation.

Greisen and pegmatoid also occur in middle Protero-zoic strata outside the contact. Nb and Ta mineralizationare found in the feldspathization and greisenizationzones in the upper part of the stock, with a tendency forTa concentrations as well as Ta/Nb ratios to increaseupwards. W and Sn minerals are concentrated in quartzveins and greisen outside the stock. The reportedexploitable minerals include columbite, microlite, tanta-lite, wolframite and cassiterite, in association withmolybdenite, galena, sphalerite, pyrite, arsenopyrite,pyrrhotite and other sulfides. In some places chalcolphileelements are recoverable.

The characteristics mentioned above are common fea-tures among the rare metal deposits of Southeast China.

The ore-forming material was obviously derived fromsedimentary rocks of the upper crust. The enrichmentprocess can be described as follows:

1) During granitization and in the presence of a con-siderable amount of fluid, Nb, Ta, W and Sn were leachedfrom the surrounding rocks, and absorbed into a melt-fluid phase because of their hydrophilic ligand affinity.

2) During crystallization of the granitic magma, suchore-forming elements behaved incompatibly due to theirhigh valencies and large radii, resulting in enrichment ofthese elements in the residual fluid-melt phase.

3) During the post-magmatic hydrothermal process,biotite and plagioclase were replaced by alkali feldspar,and some rare metals contained in those phases werereleased, resulting in the enrichment of ore-forming ele-ments in the residual fluid phase.

In all stages of the mineralization process, involve-ment of a fluid phase was critical. Because such a fluidphase is possibly supplied from a kata-metamorphiczone, the occurrence of transformation granites andrelated deposits along the NE Jiangxi Deep Fault indi-cates that some parts of the sedimentary rocks werethrust down to a depth equivalent to granulite facies.The contribution of subducted sediments is important todetermine the distribution and characters of pairedgranitic belts and associated mineralization along theNE Jiangxi A-type subduction zone.

6. Concluding Remarks

The Yanshanian granitic rocks distributed on bothsides of the NE Jiangxi Deep Fault, have remarkablycontrasting petrochemical characteristics as well as dif-ferent metal species in the associated hydrothermaldeposits. Granitic rocks and their associated depositsdistributed on the NW side of the fault, form an areanamed the Dexing-Wuyuan porphyry belt, and belong tothe so-called syntexis type, whereas those on the SE side,constitute the Damaoshan-Lingshan belt, and belong to

48 RESOURCE GEOLOGY : Y. Ye, H. Shimazaki, M. Shimizu and S. X. Hu

Fig. 6 Geological cross section of the Geyuan Nb-Ta-W-Sn deposits (modified from Bai, 1989).

transformation type. Two contrasting types of graniticrocks, syntexis and transformation, are almost compara-ble in terms of their petrochemical characteristics to themagnetite- and ilmenite-series, and the I- and S-typegranitic rocks, respectively.

The Yanshanian granitic activity in Southeast China,including that along the NE Jiangxi Deep Fault dis-cussed above, is distributed widely for over 800 kminland from the present coast, and it is obvious that thosemagmas were not produced by a single B-type, oceaniccrust to continent, subduction mechnism. Partly becauseof this reason, and partly because of the presence of a deepfault reaching to the Moho discontinuity, an intra-conti-nental A-type, continent to continent, subduction processis believed to have occurred along the NE Jiangxi DeepFault during Yanshanian time due to a strong northwest-wards compression from the Pacific side inlandward.

An idealized and simplified cross section is shown inFigure 7. The subducting continental slab released afluid phase, and first produced a H2O-rich felsic magmaby the partial melting of rocks near the boundarybetween the upper and lower crust. The magma formedthe Damaoshan-Lingshan belt southeast of the DeepFault. Further subduction of the continental slab resultedin partial melting of both the lower crust and the upper-most part of the mantle; the mafic magma produced bymelting of the mantle giving rise to the Moho disconti-nuity and partial melting of the lower crust. The magmaproduced by this machanism consists of both mantle andcrustal components, and formed the Dexing-Wuyuanporphyry belt northwest of the Deep Fault. The mineraldeposits associated with both belts have characteristicmetal assemblages reflecting the source materials oftheir respective magmas.

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50 RESOURCE GEOLOGY : Y. Ye, H. Shimazaki, M. Shimizu and S. X. Hu