3.18.1.1 Reserves and Resources

China has a vast territory and is endowed with abundant gold resources. By the end of 1986, gold exploration had been carried out for about 40 years and the gold reserves listed in the balance table of mineral reserves are 2,216 tons, 575 tons of which belong to categories A+B+C. During the seventh and eighth Five-Year Plan periods, 1,450 and 1,735.646 tons of gold were explored respectively, totaling 3,185.646 tons in the above ten years. By the end of 1997, 1,304 gold ore districts had been explored with retained reserves of4,265.52 tons, of which 1,279.85 tons belong to categories A+B+C and 2,985.67 to category D. An exact comparison between China and western countries can be hardly made because they have different classification schemes and criteria for gold reserves. Nevertheless, it is out of question that China is among the leading countries in the world in terms of explored gold reserves.    

In China, gold ore exists chiefly as primary gold, placer gold and associated or by-product gold. Among the explored gold reserves, primary ore is the major source in the production of gold products, occupying 75%~85% of the annual output (Table 3.18.1).

Table 3.18.1 Structure of gold resources in China

China has fairly good metallogenic conditions of gold deposits. Geological experts from the Ministry of Geology and Mineral Resources estimated that the total gold resources of Shandong and other 9 provinces and autonomous regions are up to 11,025 tons, while some other geologists such as Li Tong and Du Chunlin reckoned that the potential gold reserves of China are 15,000 tons. The estimation made by the Gold Geology Institute of the Ministry of Metallurgy is that there are 46 metallogenic areas and 70 prospective areas of primary gold ore with potential resources of 10,000 tons and more; and 39 prospective metallogenic areas of gold placers with potential resources of 920 tons. The above estimations show that China is possessed of abundant gold resources.

3.18.1.2 Characteristics

Gold resources are distributed unevenly in China. Many types of gold ore have been found in northern and eastern China. Primary gold ore occurs mainly in Shandong, Henan, Hebei, Shaanxi, Jilin and Hubei; while gold placers are found mainly in marginal areas of northeastern China, where stream systems are well developed, and in areas in southwestern China, such as Heilongjiang, Shaanxi, Gansu, Sichuan and Inner Mongolia. By-product gold deposits are chiefly distributed in the lower and middle reaches of the Yangtze River, such as Jiangxi, Hubei and Anhui. China is situated at the junction of the Eurasian plate, Indian plate and Pacific plate and early-stage continental nuclei are well developed in the North China block and Yangtze block. The long-term geological evolution was full of repeated and violent tectonism and magmatism, which brought about very good conditions for the formation of gold deposits (Fig.3.18.1).

(1) Stratabound mineralization of gold deposits     

The gold deposits in China show evident stratabound characteristics. This indicates that these deposits are bounded in particular stratigraphic units and more importantly that the stratigraphic units have relatively high background values of gold. According to numerous researchers, the following formations are gold-bearing strata in China.     

     1) Precambrian metamorphic basic volcanic formations

     These formations consist mainly of amphibolite, plagioclase hornblende gneiss and hornblende schist with occasional chlorite or actinoliteschist. Among these formations are the Anshan Group Sandaogou Formation, Jianping Group Xiaotazigou Formation, Badaogou Group Wangchang Formation, Jiaodong Group Pengkuang Formation in addition to the Sanggan Group, Taihua Group and Wutai Group. They are the host rocks for the following metallogenic belts respectively: the Jiapigou-Helong, Chifeng-Chaoyang, Jidong (East Hebei), Zhangjiakou, Jiaodong (East Shandong) and Xiaoqingling metallogenic belts. Gold reserves of the above ore belts make up more than 70% of the national total. Microanalysis shows that these stratigraphic units have relatively high background values of gold. Their protoliths are analogous to basic volcanic rocks featuring younger ages and higher degree of metamorphism compared with the greenstone belts in Canada, South Africa and western Australia. The metallogenic epochs are the Hercynian and Yanshanian. In the above metallogenic belts, apart from meta-basic igneous formations gold ore also occurs in relatively young stratigraphic units or granitic intrusions in some cases, only the source beds are still basic volcanic formations. The Yu'eryan ore district in the Jidong belt can be an example.

     2) Metapelitic clastic rock formations

     Their protoliths are shale or sandstone which then are metamorphosed into slate, phyllite, schist and metasandstone in addition to quartzite and sericite-quartz schist. These rocks contain more or less organic carbon and primary sulfides. Such formations include the Heilongjiang and Mashan Groups in the Jiamusi block, Liaohe Group in East Liaoning, Zhuzhangzi Group in East Hebei, Waitoushan Formation in Tongbo, Henan Province, Benxi and Lengjiaxi Groups in West Hunan, Cambrian Shuikou Group in East Guangxi, Cambrian Bacun Group in West Guangdong, Sinian Silun Group in Guangdong, Pre-Devonian Chencai Group in Zhejiang, Middle Devonian Gudaoling Formation in the Qinling folded zone, Cambrain Sandu Formation in Guizhou, Triassic Luolou and Xinyuan Formations in the Qinglong-Cexiang area in Southwest Guizhou and some gold-bearing horizons in the Tianshan folded zone. They serve as host rocks respectively in the Jiamusi-Mudanjiang metallogenic belt, Dandong-Yingkou metallogenic belt, Tongbo metallogenic belt, Xiangxi (West Hunan) metallogenic belt and Guidong (East Guangxi) metallogenic belts. Such stratigraphic units usually show relatively high background values of gold and therefore are source beds of gold ore, which were formed as meta-basic volcanic formations and associated gold ore were subjected to weathering, denudation and redeposition.

     3) Spilite-keratophyre formations     

     Such formations consist of spilite and keratophyre with low degree of metamorphism and texture of volcanic rocks. The following stratigraphic units belong to these formations: the Xiong'er Group in the Qinling area, Bikou Group in South Gansu, Yuelinghe Group in South Shaanxi, Shuangxiwu Group in Zhejiang, and Wudang Group in Northwest Hubei, where not only simple gold deposits, but also massive sulfide deposits associated with gold have been discovered, such as the Baiyinchang and Xiaotieshan copper deposits in Gansu, Xiqiu copper deposit in Shaoxing, Zhejiang Province.4) Andesite-rhyolite volcanic formations     

    These formations are composed mostly of Meso-Cenozoic intermediate-acidic volcanic rocks, including gold-bearing volcanic rocks in the Taiwan gold district, Upper Jurassic volcanic rocks in the Yanbian area, Jilin Province, Upper Jurassic Dawangshan Formation in the Ningwu-Lishui basin, and Upper Jurassic Moshanshi Formation in the Suichang-Longquan area, Zhejiang Province. The gold ore in these districts has high content of silver, so there occur commonly gold-silver deposits. Gold is usually associated with copper in the Tongjing gold deposit in the Nanjing-Wuhu area, Jinguashi gold deposit in Taiwan and Xiaoxinancha gold deposit in Jilin. 

     To sum up, most of the primary gold deposits in China occur in particular gold-bearing formations of a particular structural setting. Deposits (occurrences) are distributed concentratedly as belts or clusters. The deposits extend in directions coincident with the general strikes of the local strata, among which Archean strata are predominant while Proterozoic, Paleozoic and Mesozoic strata are less important. These are all gold-bearing strata, but developed in varied degrees. The mineralized wall rocks include metamorphic, sedimentary and igneous rocks. The gold abundance of these mineralized rocks is generally several times or dozens of times as large as that of the same rocks in the crust. Most gold orebodies and their host rocks have similar isotopic compositions. The above features show that stratabound mineralization is typical of the gold deposits in China.

(2) Control of granitic magmas on gold mineralization

Spatially gold deposits are associated with granitic intrusions with some deposits occurring even inside the intrusions or contact zones. This suggests that magmatism is an active factor responsible for gold mineralization.     

Modern petrology divides granitoids into two types according to their geneses: mantle-derived granites and crustal remelting granites. However, many available data show that granites closely related to gold mineralization were formed through remelting and regenerating of basement metamorphic rocks. Such gold deposits have been found in Shandong, Liaoning, Jilin and Guangdong provinces.     

Gold mineralization belts are linked with intersections of deep-seated faults controlling various mineralizing and magmatic processes, implying that gold-bearing substances beneath the crust participate in the mineralization. In nickel, cobalt and platinum deposits related to ultrabasic rocks there is a high content of gold and even individual gold orebodies can be formed. Convincing cases are the Mojiang gold deposit in Yunnan, Xiaosongshu'nangou deposit in Qinghai and the Toli deposit in Xinjiang, where gold ore is associated and genetically related with ultrabasic rocks.     

Available data and results show that magmatic rocks of three ages, i.e. Caledonian, Hercynian and Yanshanian, are typically related to gold mineralization. ¢Ù The Caledonian granites are mainly distributed in Caledonian geosynclines in South China and consist chiefly of porphyritic granodiorite, granite-porphyry and quartz porphyry. For example, the Daning rockbody have gold contents of 9 ppb and 3.7 ppb in biotite diorite and porphyritic granodiorite respectively. The Longshui and Zhanggongling gold deposits were formed around the contact zone of the rockbody and Cambrian strata. ¢Ú The Hercynian magmatic rocks are mainly distributed in Hercynian folded zones in northwestern and northeastern China. Ore-controlling rocks are predominantly plagiogranite, granodiorite and monzogranite of the middle and late Hercynian, all of which occur as batholiths, stocks and apophyses. Statistics show that more than 50 gold deposits (occurrences) have been discovered and they occur mostly within rockbodies or near contact zones. ¢Û A great number of endogenic gold deposits in China, especially in eastern China, are related with the Yanshanian tectonic magmatism. For instance, the reserves of such gold ore in western Liaoning Province account for 22% of the total reserves of the province. In the Yanshan area, the Yu'erya, Baizhangzi, Jinchangyu and Sanjiazi gold deposits are all related to small Yanshanian intermediate-acidic intrusions. The Yanshanian Huashan and Niannianshan intrusions outcrop from east to west in the northern part of the Xiaoqinling gold field in Henan Province and analysis of samples of heavy concentrates shows that these intrusions are gold-bearing ones and there occur even gold-bearing quartz veins in some places.

(3) Control of tectonics on gold mineralization

     1) Plate tectonics and gold mineralization

      Plate tectonics and gold mineralization are closely related with each other because the accretionary zone of a plate (oceanic rift) serves as a passageway from mantle to crust although most of the gold there is just dispersed in rocks except for several gold-associated massive sulfides deposits. Only when such newly formed oceanic crust is pushed towards a subduction zone and vanishes and remelts, would gold be concentrated most likely to form ore. Remelting of the oceanic crust brings about calc-alkaline volcanic-intrusive rocks to give rise to the formation of contact metasomatic, porphyry, explosion-breccia and volcanic and sub-volcanic gold or gold-silver deposits.

      The major gold ore belts in China are largely distributed on the margins of old plates and in old island-shaped uplifts near suture boundaries; for example the Yinshan-Yanshan metallogenic belt and Qinling-Dabieshan metallogenic belt are controlled by the uplifts of the suture boundaris on the northern and southern margins of the North China plate respectively. Besides, uplifts such as anteclises and geosynclinal anticlinoria within the plate take control over the distribution of secondary metallogenic belts (provinces) or mineralized areas. For example, the Jianping uplift, Jiaodong uplift and Wufeng uplift in the North China plate are all areas where gold deposits are concentratedly distributed.

     2) Control of host structure on gold mineralization

      (a) Faulted structure: Most of gold ore deposits are hosted in faulted structures, which can be divided into different types according to their mechanical properties, such as extension, tenso-shear, compresso-tension and tenso-compressive fractures. Most of gold ore in Archean meta-basic rocks and part of gold ore in Paleozoic and Mesozoic strata are controlled by faulted structures.

      (b) Folded structure: Other important structures for the formation of gold ore deposits include saddles and hinge zones of anticlines and troughs of synclines as well as interstratified rupture zones, joints and fractural systems caused by folding. The examples are the Sidaogou and Baiyun gold deposits in Liaoning, Yindongpo gold deposit in Henan, and Woxi gold deposit in West Hunan. It is a distinctive feature that gold deposits occurring in Proterozoic and Paleozoic argillaceous clastic formations in China are controlled by folded structures.

      (c) Volcanic structure: Circular or radial faults around calderas, volcanic necks, volcanic breccia pipes and other irregular faults around craters are major ore-controlling structures of gold (silver) deposits related to Mesozoic and Senozoic volcanic and subvolcanic rocks. The Ciweigou, Wufeng, Wuxingshan and Xiaoxinancha gold deposits in Yanbian, Jilin Province, Yinkengshan, Babaoshan and Dalingkou gold deposits in Zhejian Province and gold and gold-silver deposits in Hongshan, Hebei Province are typical cases.

      (d) Explosion-breccia pipe: The explosion-breccia pipe due to hypabyssal intrusion is also one of the host structures of gold ore, such as gold deposits in Qiyugou, Henan Province, Gengzhuang, Shanxi Province, Shuiquan, Liaoning Province, and Yangjishan, Jiangxi Province. The Tuanjiegou deposit in Heilongjiang and Qibaoshan deposit in Shandong are commonly considered as porphyry gold deposits, but most of the gold orebodies are hosted in explosion-breccia.

      (e) Host rocks with favorable physical and chemical properties: Host rocks are generally brittle and easily fissured or have high porosity. Such rocks are active chemically and apt to corrosion and metasomatism. Veinlet-disseminated (Carlin-type) gold deposits and some contact metasomatic or by-product gold deposits are just those controlled by this structural mechanism. 

     Apart from the above features, one can see that numerous types of gold deposits but only a very small number of large and superlarge ones have been found in China. As for the ore quality, there are less rich ores but more medium-grade ores and the ore grade varies greatly. Medium- to low-grade primary gold deposits with the grade£¼6 g/t make up 83% of the total number of gold deposits, while placer gold deposits with grade£¼0.25 g/m3 make up 66% of the total number of gold placer deposits. On the whole, the grade of both primary and placer gold is rather low and the reserves of rich ores are very limited in number. Furthermore, a certain amount of explored primary gold is very fine in grain and contains arsenic or mercury, so the dressing and smelting are rather difficult. Although some deposits of this type have been mined at present, they have only a low recovery ratio and poor economic benefits. Besides, environment pollution is a critical problem. Therefore, how to effectively utilize this portion of gold resources awaits further study.