Dongqiao Chromite Deposit in Amdo County（4）
The Dongqiao chromite deposit is located 90 km to the west of the Amdo County town at an elevation ranging 4400-4800，accessible by highways.
The deposit occurs in the Dongqiao ultramafic massif which is 17.4 km long from east to west and the broadest portion from north to south being 3.9 km，covering an area of 45 square kilometers.The massif is composed mainly by harzburgite.Dunite is displayed as uneverily distributed shlierens of differ-ent size and irregular in shape.It is comparatively concentrated in the middlepart and forms a dunite-dominated lithofacies belt.Altogether 1 29 chromite localities（groups）have been found，among which 5 localities including about 18 orebodies were of commercial significance.The largest No.1 7 ore group oc-curs in the middle of the massif，being made up of four large orebodies which are lenticular，stratiform-like，irregularly chambered，etc.The chromite ores are mainly massive，allotrimorphic and coarse-grained with Cr2O3 exceeding32%and Cr/Fe greater than 3，belonging to metallurgical ores.The reserves proved amounted to 457000 tons and the deposit is of small size.
In August 1 9 5 9 Liu Tingrong of the Zangbei Geological Party led a sub-party to investigate the salt lake in Zigtangcuo and discovered the Dongqiao ul-tramafic massif on the south bank of the lake.When the salt lake investigation was over，he organized all the staff to search for chromite in the mountains.As a result，three chromite localities were found.In their report on the salt lake investigation they indicated that“The massif is widely distributed from Amdomaima（now the Amdo County town）on the east up to the Qilin Lake on the west with an intermittent length of over 1 00 km.It consists mainly of dunite associated with chromite and deserves further work”.This information had undoubtedly laid the foundation for chromite prospecting in northern Ti-bet.
Based on the above information，the Tibet Comprehensive Expedition Team of the CAS carried out a primary investigation on the Dongqiao ultramaf-ic massif in June 1960.They compiled a sectional lithofacies map and a 1∶25000 geological sketch map and found 17 orebodies.In September，according to the materials of the CAS，the Zangbei Geological Party of Tibet made a pre-liminary survey of the orebodies，compiled a 1∶10000 geological sketch map of the central and east sectors，revealed the major bodies by trenching in a more systematic way，and calculated roughly the ore reserves at 49600 tons.In 1961 the Team collected supplementary materials from the massif and pub-lished a book entitled“Investigation of some principal chromite-bearing ultra-mafic bodies and chromite deposit of Tibet”.
In March 1 965 the Xinjiang Chromite Campaign Headquarters of the MGMR set up in Urumqi the Tibet Chromite Prospecting Group consisting of eight geologists including Han Gengcheng，Zhong Lin and others.The group worked for 1 60 days and more in Dongqiao and compiled a 1∶25000 geological reconnaissance sketch map.They revealed the surface orebodies by trenches and shallow wells，and suggested that“As the deposit is of certain scale，its ores are of good quality，and its location is easily accessible，we recommend it as a target area of chromite deposit”.Since then an all-round prospecting pro-gramme of the Dongqiao chromite deposit began.
In March 1 966 the Ministry of Geology and Mineral Resources transferred from Xinjiang，Inner Mongolia and elsewhere 200 andmore scientists and technicians，cadres and workers specialized respectively in geology，hydrogeol-ogy，geophysics，mapping，rock and mineral testing and analysis，drilling，pitting，etc.and established the Tibet Chromite Deposit Prospecting Party.Zhou Yiyuan was appointed the chief geologist in charge of the comprehensive geological survey in Dongqiao.By drilling，trenching，underground workings as well as gravitational and magnetic surveys they found successively the No.105 and the No.106 two large concealed orebodies on the west of the No.17 ore group and on the south of the No.21 ore group.They confirmed the commercial values and thereby laid down asolid ground for further work.
In 1967 the Ministry of Geology and MineralResources continued to transfer from Xinjiang，Inner Mongolia，Qinghai，Jiangxi and other provinces 1200 and more persons specialized in various subjects to Tibet and established the No.2 Geological Party of Tibet.The party carried out 1∶10000 geological reconnaissance and geological，hydrogeological and geophysical surveys as well as the corresponding topographic survey，analysis，testing，etc.；while for the two major ore groups，No.1 7 and No.21，they conducted detailed survey and preliminary exploration.In 1969 and 1971 it submitted respectively the“Report on reserves of the No.17 ore group in the Dongqiao chromite district，Amdo County，Tibet”and the“Report on reserves of the No.4，6，8 and 9 ore groups in the Dongqiao chromite district，Amdo County，Tibet”.A total of 457000 tons of chromite ore reserves were proved.Thus the prospecting evaluation of the deposit was completed but thework in the mining district was still on.
After 1972 the No.5 Geological Party of the TBG，the Chinese Academy of Geological Sciences，the Chengdu Institute of Geology and Mineral Re-sources of the MGMR and other institutions carried out supplementary reveal-ing work for other orebodies of the massif and traced them by drilling.To sum up the experience，they studied the ways for finding medium-and deep-seated ores.They also researched the associated platinoid metals and provided a re-serve of 384.6 kg.The prospecting and exploration work had been continued until 1979 with some in-depth knowledge gained of the characteristics of the deposit，the inner structure of the massif and so on，but unfortunately no breakthrough was made in finding new orebodies.The footage of drilling amounted to 14225 m.
The Dongqiao chromite mine was built by the Industry Department of the Tibet Autonomous Region in cooperation with the Wuhan Iron&Steel Works，and the No.17 ore group was put first into production in 1971.The reserve of the designed area was 330000 tons.Until its closing in 1983 the mine yielded 310000 tons of ores.Under the situation when the channels of chromite impor-tation was then blocked，the exploitation of the Dongqiao chromite mine solved to a certain extent the nation＇s urgent need；besides，the Tibet Autonomous Region had obtained great economic benefits from it.
掌服可益： Dongqiao Town, Pu Tian Xiu Yu District, Fujian Province. 有的地名必须用拼音
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