加拿大拉布拉多地槽DSO型铁矿床成矿规律及找矿方法研究

Ore-forming processes and exploration methods of DSO iron deposits in Labrador Trough,Canada

DSO(Direct Shipping Ore)型铁矿床即直运型铁矿床,指加拿大拉布拉多地槽区Fe品位大于50%(w(SiO2)<18%)的赤铁矿矿床,因其矿石品位高、经济效益突出而备受关注。对该地区DSO矿床区域成矿背景、典型矿床研究表明:(1)DSO矿体均赋存于苏克曼组含铁建造中;(2)DSO矿体的产出位置主要受构造控制,构造为热液流体的运移提供了通道,也为矿质的重结晶及沉淀提供了空间;(3)软质DSO成因属深部热液-表生改造型,硬质DSO成因则属热液型。根据DSO的成矿特点,可将拉布拉多地槽DSO找矿靶区分为谢弗维尔软质DSO找矿靶区、铁矿湖-阿提卡玛根软质DSO找矿靶区和阿斯特雷—索耶湖硬质DSO找矿靶区。找矿实践中,应通过地质填图、物探等方法对拉布拉多地槽中部地区的岩性和构造进行控制,重点关注NW向大断裂与次级断裂、次级褶皱、玄武岩与含铁建造岩性转换面的叠加处和地球物理低磁高重区。综合地质和地球物理方法优选靶区进行槽探、钻探相结合的快速验证,可有效提高找矿效率,实现拉布拉多地槽区DSO找矿工作的快速突破。

DSO （Direct Shipping Ore） deposits, the high-grade iron ores （w（Fe）〉50%, w（SiO2）〈18%） in the Labrador Trough of Canada, attracted much attention for the high-grade and significant economic benefits. By studying the geology setting of DSO deposits and the characteristics of typical DSO deposits in the region of Scheffervill,we found that： （1）all DSO deposits are hosted by Precambrian Sokoman iron formation; （2）the structure is considered to be the most important factor that influence the location of the DSO deposits, and preparing the access to deep-hydrothermal fluid and developing enough space to concentrate new recrystallized minerals; （3）the genesis of soft DSO is related to supergene-modified hydrothermal model, while hard DSO only related to hydrothermal model. According to the characteristics of ore-forming processes, we divide the DSO targets of Labrador Trough into 3 zones： the Scheffervill soft DSO zone, Lac Le Fer-Attikamagen soft DSO zone and Astray Lake-Sawyer Lake hard DSO zone. Exploration activities should focus on the areas where the secondary extensional-faults, folds and the contact surfaces between basalt and iron formation intersect the NW striking regional faults, especially when the areas also have the geophysical characteristics of low magnetic-high gravity. Synthesize information of geology and geophysics to figure out the best points to mark as reconnaissance trenching and drilling stage, which can greatly improve the efficiency of prospecting.