Duobaoshan porphyry copper deposit, situated in Nenjiang County of Heilongjiang Province, Northeast China, lies tectonically in the M ongolian-Okhotsk geosyncline. Duobaoshan porphyry copper ore field consisting of Duobaoshan copper deposit and T ongshan copper deposit contains rich copper associated w ith molybdenum, gold, silver and osmium (Os187).In this sense, this porphyry copper ore field w ill turn into a large industrial base of copper, gold, silver and osmium.At present, in Duobaoshan porphyry copper deposit occurs a usable B+C+D grade reserve of 3276630 ton Cu, 122920 ton Mo, 87 ton gold and 1417 ton Ag.
GENERAL ECONOMIC GEOGRAPHY
Shankuanggou copper deposit under mining is located in the northw estern portion of Duobaoshan copper orefield, and in the southern portion of Heibaoshan-Murqi coalfield.Up to now, the Heibaoshan coal deposit, No.151 coal deposit and Murqi coal deposit all have been established.Guanniaohe quality marble deposit is located in the southw estern portion of the orefield.The Nenjiang River located in the w estern portion of the orefield provides the orefield with industrial water.The state electrical wire net passes through the western portion of the orefield, providing the development of orefield with electric energy.
GEOLOGIC FEATURES OF OREFIELD
Duobaoshan copper orefield is located in the northeastern potion of Daxing ' anling geosynclinal fold zone and on the northw estern side of Xinkailing deep fracture (Fig. 1).
The marine strata 7500 meters thick from the Low er Ordovician to the Low er Devonian, the marine and continental alternating strata 2300 meters thick from the Middle Devonian to the Lower Carboniferous, and the continental volcanic rocks and tuffs in the Carboniferous and Jurassic and the coal seams in the Upper Jurassic are exposed in the Duobaoshan deposit and its vicinities.The Duobaoshan Formation about 5000 meters thick is the most widely exposed strata in the ore field.The andesite of the lower section of the Duobaoshan Formation is the host rock of the top part of the main orebodies, w hile the upper bottom part of the main orebody is hosted by the grit unit of the Upper Tongshan Formation.The mean copper contents in Tongshan and Duobaoshan formations are 80×10-6 and 130×10-6, respectively.
Intrusions
The intrusive rocks well developed in the region consist largely of granodiorite, plagiogranite and quartz diorite, and are divided into middle Caledonian, late Variscan and early Yanshanian cycles.
The intrusive rock exposed within the mineral deposit is a compound body composed mainly of granodiorite closely related with mineralization, granodiorite-porphyry, post-minera-lization oligogranite and quartz diorite.
The Duobaoshan granodiorite body.The surface of the body is the shape of cyrtospirifer.This body extends along NW-SE, with its dip SW, and the angle of dip 60°, show ing a tendency to enlarge dow nw ard.T he boundary lines contacting the wall rock are clear, most of which are jagged.All the wall rocks are hornfelsized and biotitized in varying degrees.The terrain is mainly composed of granodiorite and plagioclase granite w ith the former distributed inside the body, and the latter distributed on edges of the body.Dike rocks associated with them are hornblende-diorite porphyrite and aplite quartz diorite.The granodiorite is greyish w hite, light grey-green, most of which show the hypidiomorphic granular texture. This rock is composed by 57.8% plagioclase, 21.0% quartz, 11.5% perthite, 10.0% trap mineral and0.2% sulphide.When the potash feldspar perthite reduces, it will change into plagioclase granite.Compared with the same kind of rock in our country, this rock show s few er content of Si and Ca, but similar features in other aspects.Compared with the same kind of the rock in Daili, this rock show s less content of Si and Ca.The accessory mineral combination is composed mainly of zircon-apatite-titanite-magnetite.
Granodiorite-porphyry body.This body is exposed in Dalazi situated in the middle of Duobaoshan mineral deposit. On the ground, this body is principally divided into two lenslike NE-distributed terrains whose dip is SW with the dipping angle 75°-80°.They pitched downw ard tow ards NW to merge into one body and show ed a tendency to enlarge.T his body has intruded into the granodiorite w ith its interface revealing a jagged, and its shape complicated in the contact position where the granodiorite is obviously smashed, leaving a metamorphic ring 3-10 centimeters wide.The grey-white rock has its porphyritic texture.The matrix has its microgranitic texture.In the microlite, the quartz and plagioclase are predominant, and the perthite and biotite are placed the second.
It is suggested that both intrusions originated in an island-arc environment and that their emplacement occurred along the tectonic moving zone of an accreted continental margin during the organic process.Granodiorite-porphyry in the district is rich in Si, but poor in Fe2O3, Al2O3 and CaO obviously, compar w ith those in Dexing, Fujiaw u.T he reason for the enrichment of Si is probably that the rock contains more tiny quartz dyke later.
Duobaoshan ore field located in a large-scale anticline submerged in the NW direction contains intensely-developed fracture structure.On the west side of the ore field exists a northeastern-trending compression-shearing megafault, deforming the northw estern structural belt into a north-w esttrending arcuate structure within a ten kilometer-wide area adjacent to the megafault.The arcuate structure forms the basic tectonic framew ork of the ore field, whose area broadly coincides with that of the arcuate structure.On the arcuate structure are superimposed not only the WNW-trending and NNW-trending structures, compression-shearing fractures and schistosity, but also the secondary NE and NNE-trending, and latitudinal and longitudinal structures.Duobaoshan deposit is just located at the junction of multiple structures.
Alteration
The alteration zonation of the ore deposit is attributed to the superimposition and modification of multiple hydrothermal activities associated with magmatism.Generally speaking, the pre- and post-granodiorite porpylitizations form the outer zone, and the syn-and post-granodiorite porphyry potassic alterations (subdivided into intense silicification subzone, Kfeldspar-quartz subzone and K-feldspar-biotite subzone) constitute the inner zone around the porphyry body.The majority of the oblate-ring-like sericitization area is superimposed on K-feldspar-biotite subzone and the minority of the same area is superimposed on propylitization zone to form the intermediate zone.Carbonatization areas in the form of bands crosscut all other zones.
Mineralization
The migration and emplacement of copper in Duobaoshan deposit is the result of repeated hydrothermal activities.Biot-i tization gave rise to the initial enrichment of copper, while the sericitization and carbonatization further enriched it, resulting in the formation of present orebodies and mineralized zones of the deposit.
The orebodies and mineralized zones around the porphyry body and potassic alteration zone are distributed in the sericit-ization zone that in turn is superimposed on biotitization zone. The occurrence mode of orebodies and mineralized zones roughly coincide with that of porphyry dyke-like body.
There are four mineralized zones in the deposit, among which the Nos.2, 3 and 4 occur in the hanging wall of the porphyry body with only No.1 at its footw all.The northw estern submerged part of the porphyry intrusion w here are located Nos.1, 2 and 3 mineralized zones is more intensely altered.How ever, in the mineralized southeastern part is hosted No.4 mineralized zone.Tongshan ore deposit consists of four ore bodies, too: No.Ⅰand Ⅱ ore bodies are located in the hanging wall of the T ongshan fault, and distributed along NW, with their dip SW, and most of their dip angles more than 60°.No.Ⅲ and No.Ⅳore bodies are located in the hanging wall of the fault, and distributed along the near-EW (Fig. 2).
Figure
2.
Sketch of the geological section relation in Duobaoshan copper deposit.③.Number of ore zone; α.andesite; S. sericitization belt orebodies; P.propylitization belt; γδ.granodiorite; γδπ.granodiorite porphyry; γ.oligoaranite; Q. K-silicification belt-geological boundary and altered boundary.
The mineralized zones consist of orebody group.The large orebodies range from 200-400 m in thickness and are 1000 m or more in length and depth.In both the hanging walls and footw alls of the large orebodies occur subordinate banded ores and lenses.
In the main mineralized zones sulfides exhibit the good zonation.The bornite predominates in the central part of the large orebodies, but it decreases outw ard w ith the increasing chalcopyrite until the latter turns into an essential mineral. The pyritic zone occurs in the vicinity of the offset shoots of large orebodies.The zinc mineralization zone is occasionally distributed around the outer rim of the pyritic zone.
ORE COMPOSITION
The dissemination is the major textural type of copper ores with the dissemination-veinlet type, the minor textural type (Fig. 3).
Figure
3.
Sketch of geological sections in Tongshan copper deposit.1.Duobaoshan Formation; 2.Tongshan Formation; 3.granodiorite; 4.orebodies; 5.Tongshan fault.
The veinlets are developed mainly at the cupola of orebodies and intersection of structures.The ore mineralogy is characterized by the simplicity of metallic sulfides, complexity of trace elements, comparative rarity of typical gangue minerals.74 kinds of minerals have been identified, 36of which are metallic and 32 of which nonmetallic.The principal ore-forming minerals are chalcopyrite, bornite and molybdenite, followed by chalcocite and tetrahedrite.The secondary copper minerals are malachite, azurite, tenorite, covellite and chalcocite.The native gold and silver, and argentite are know n to be extractable as by-products.Oxidized ores account for only 1%-2% of the total reserves.(The main gangue minerals identified are quartz, sericite, penninite, epidote, calcite, biotite, K-feldspar and albite, associated with hydrobiotite, diopside, ankerite, muscovite, andalusite, tremolite, actinolite, actinolite, aolinite, anhydrite, montmorillonite, zeolite, chlorite, illite, sillimanite, grpsum and garnets).The associated economic components of the deposit are Mo, Au, Ag, Re, Se, Os, Pt, Pd, Ir, etc..Au and Ag mostly occur as individual minerals associated w ith sulfides.By monomineral assaying the main Au-and Ag-bearing sulfides are bornite with chalcopyrite and molybdenite as minor carriers.
The pilot test of the ore shows that Re and Os are enriched in molybdenite concentrates, while the other economic components can be extracted as by-products from copper concentration.
The ore industrial types are disseminated ore, veinlet-disseminated ore and veinlet ore.There are not obvious boundary lines among them.Generally, most of the disseminated ores are distributed over the middle of the ore body.Veinletdisseminated ores are distributed most widely in the mine. The veinlet ores are very few, and mostly distributed at the top and edge of the mine.The chemical composition of the ore are composed of 35 elements such as Cu, M o, Au, Ag, Se, Re, Pb, Zn, Co, Ni and Bi, As, of which Cu, Mo are abundant enough to be an industrial ore body, and of which Au, Ag, Se, Re and Mo have met the industrial need as accompanied useful elements.
POTENTIAL VALUE OF Cu, Mo, Au, Re AND Os187 IN OREFIELD
The orefield has a reserve of 3276630 tons copper, 122920 tons molybdenum, 87 tons gold, 1417 tons silver and 20060 tons molybdenute.The molybdenite contains a reserve of 24 tons Re, 1247 kilograms Os187 and Pt, Pd, Ir.
The value of w(Cu)/w(Mo) in ores is 32 in Duobaoshan copper deposit and 29.41 in Tongshan copper deposit.In the mine, the content of w(Au) in one-ton copper ores is 32 g/t in Duobaoshan, and 18 g/t in Tongshan.In addition, the content of Re in one-ton molybdenum ores is 917 g/t in Duobaoshan, and 1801 g/t in Tongshan.
In 1995, the content of Os187 was found to be higher.In 1996, 250 specimens were collected and tested w ith the result that the average grade of w (Os187) was 5.14 g/t (molybdenite) in Duobaoshan copper deposit, 7.1 g/t (molybdenite) in Tongshan copper deposit.T he value of Os187 in the orefield is at present the highest in the w orld.In some sectors, Pb and Zn have turned into industrial ore bodies, but their scales are small.Such elements as Co, Mn only are related with the mineralization.
Figure 2. Sketch of the geological section relation in Duobaoshan copper deposit.③.Number of ore zone; α.andesite; S. sericitization belt orebodies; P.propylitization belt; γδ.granodiorite; γδπ.granodiorite porphyry; γ.oligoaranite; Q. K-silicification belt-geological boundary and altered boundary.
Figure 3. Sketch of geological sections in Tongshan copper deposit.1.Duobaoshan Formation; 2.Tongshan Formation; 3.granodiorite; 4.orebodies; 5.Tongshan fault.
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