Abstract:

The tectonic setting, ore-forming time, metallogenic mechanism of nineteen molybdenum deposits and four gold deposits and their relationship with the Indosinian intrusions, located along the northern margin of Northern China craton (NCC) and adjacent area, have been discussed. Their geographic sites are different, but most of them occur in Precambrian metamorphic rocks and Early Paleozoic volcano-sedimentary rocks, and show intimate spatial and temporal relations with the Indosinian granitoid intrusions. Although the ore-forming process of molybdenum deposits last from Early to Late Trassic, but the large-scale mineralization event occurs from 230 Ma to 220 Ma. The ore-forming process of the gold deposits occurs prior to the “peak time” molybdenum mineralization (230 Ma to 220 Ma). Most of ore-forming age data change from 245 Ma to 239 Ma. Mineralization occurred in Mo and Au deposits locality as dissemination, stockwork, veinlet and vein group as well as replacement along the different fracture zones. Mo deposits can be classified as two types: porphyry and skarn. Au deposits can also be divided into two groups: vein and replacement body. Mineralization was likely formed by filling of ore-bearing fluids or hydrothermal replacement within the reactivated fault or fracture zone. Studies show that the lithospheric and crustal extension prevailed along the northern margin of the NCC following the collision of Xing-Meng amalgamated block and NCC during the period of Latest Permian to Late Trassic period. The post-collisional/post-orogenic extensional activities resulted in the formation of several E-W-trending fault zones, and widespread alkaline or high-K calc-alkaline intrusions. Intensive extension and magmatic activities provide favorable dynamic force and ore-forming material sources for molybdenum and gold mineralization. The identification of Indosinian molybdenum and gold mineralization should encourage renewed mineral exploration aimed at the discovery of blind deposits along the northern margin of the NCC and its adjacent area. The altered and brecciated Indosinian granitoid intrusions may be the favorable exploration targets.

Key words: molybdenum deposit, gold deposit, ore-forming process, Indosinian, magmatic activity, extension, northern margin of North China craton