Geology, Geochemistry And Discussion On The Origin Of The Qiaoxiahala Fe-Cu-Au Deposit In Xinjiang

Iron ore resources in China are abundant, and its present measured ore reaches 59.3 billion tons in China, but the domestic iron ore products still can't meet the requirement from the steel industry and the import of iron ore is becoming larger and larger. Iron ore resources in Xinjiang, Northwest of China, mainly concentrate in the Tianshan, Altay and Kunlun-Aerjin mountain areas, and that in Altay occupy 13% of all in Xinjiang. However, considering the whole domestic supply-requirement situation in China, Xinjiang steel industry needs to depend on its own iron resources, due to its own long distance from the most provinces for transportation. The Qiaoxiahala Fe-Cu-Au deposit, locating in the southeast of Fuyun county in Altay, has developed from a small-scale iron deposit at 50's into a middle-scale Fe-Cu-Au deposit at present. According to its drill hole data, it's still quite potential to enlarge its resources because the orebodies in the drill hole do not end yet.Besides meeting the need of iron ores, the Qiaoxiahala Fe-Cu-Au deposit is significant in the theory research. After the searches of vast references, there are very few references on iron deposits correlated to picrite. Although this kind of deposits are few, it does exists, such as the Afton Cu-Au deposit related to picrite found in Canada. The Qiaoxiahala deposit can set an example for the research on iron deposits correlated to picrite, and is also the first iron deposit related to picrite which has been reported in China. At present, Fe-Cu-Au are the major profitable metals in the Qiaoxiahala mine, but highly enriched REE in the chalcopyrite ore is also very potential. It's important to research on this combination of Fe-Cu-Au-REE, as we've known the world class super-large deposit of Olympic Dam Fe-Cu-Au-REE deposit in Australia. The author has done the field work in the Qiaoxiahala mining district and its periphery like the Laoshankou area, and nearby iron deposits such as Mengku, Abagong, Jiebiete. The author further assisted with making four profiles on the site of the Qiaoxiahala mining district and the Laoshankou area, collected 250 samples of rocks and 48 of ores, described the polished thin sections, tested samples for major and trace elements by X-ray fluorescence and ICP-MS respectively, for magnetite, chalcopyrite and tourmaline by electron microprobe, for sulfide by sulfur isotopes and carbonate by carbon-oxygen isotopes, and for hornblende from the diorite by Ar-Ar dating.Here are some conclusions:1. On the aspect of typical ore deposit:Through various works of field survey, profile measurement, rock/ore identification and geochemical analyses,①"the Qiaoxiahala Formation"is suggested to be named as a suite of picrite and trachyte occurring as the footwall and divided from the Middle Devonian Beitashan Formation;②a new type of iron ore deposit correlated to picrite perhaps exists in the north margin of Junggar fold system, providing a new guide for prospecting of iron;③highly enriched REE in chalcopyrite ores in Qiaoxiahala can present a good example for research on Fe-Cu-Au-REE metallogeny as it is similar to the Olymoic Dam deposit partly.2. On the aspect of metallogenic epoch:Through different methods of isotope dating,①the 40Ar/39Ar plateau age of hornblende from diorite in the western Qiaoxiahala mining district was at 378.1±3.6 Ma and its 39Ar/40Ar-36Ar/40Ar inverse isochron age at 382±17 Ma by the stepwise heating dating; based on the occurrence of diorite as cutting the iron ore bed, it is suggested that the diorite was formed later than the iron ore bed, namely the iron formation ended before 380 Ma±;②due to various causes such as the impure single minerals, dating data of Rb-Sr isochron age of magnetite and Sm-Nd isochron age of chalcopyrite were not coincident with field geology, but they did indicate two stages of Fe-Cu mineralizations.3. On the aspect of metallogenic region:①Through the comparison to the similar deposits home and abroad, especially in Xinjiang and Aletai, it's suggested that there's no strict limitation to prospect iron ore deposits only in Tianshan and Altay Orogen of Xinjiang;②the north margin region of Junggar fold system is indicated to be a potential area for the iron ore prospecting.4. On the aspect of geochemistry and metallogenic mechanism:①The Qiaoxiahala Fe-Cu-Au deposit is supposed to be marine volcanic-sedimentary style plus the later hydrothermal superimposition and alteration style;②Fe and Cu-Au were formed by two major periods of mineralizations: the earlier marine volcanic-sedimentary mineralization formed magnetite and the later hydrothermal superimposition and alteration enriched the magnetite and formed the Cu-Au orebodies;③Fe mainly came from the volcanic magma as the same as the footwall basic volcanic rocks, whereas Cu-Au derived from the intermediate-basic dioritoid intrusive rocks and extracted from the ealier basic volcanics, and these two kinds of rocks might share a same deep magma chamber.5. A metallogenic model of the Qiaoxiahala Fe-Cu-Au deposit has been set up and a deposit type has also been established-the Qiaoxiahala type Fe-Cu-Au deposit.6. It is suggested to expand the deep prospecting of the Qiaoxiahala Fe-Cu-Au deposit, and also further the prospecting for the Qiaoxiahala type Fe-Cu-Au deposits in the Laoshankou area and the eastern area distributed by the Qiaoxiahala Formation.