Sun Aiqun

The Isotopic Composition of Noble Gases in Gold Deposits and the Source of Ore- Forming Materials in the Region of North Hebei, China*

The source of ore-forming materials has long been a controversial focus both in metallogenic theory and in ore-searching practice. This study deals with the helium and argon isotopic characteristics of pyrites from 11 gold deposits and some country rocks in the gold mineralizationconcentrated areas within the three mantle-branch structures in the region of North Hebei Province. It is indicated that3He/4He ratios in the gold deposits are within the range of 0.93 × 10−6 –7.3 × 10−6, with an average of 3.55 × 10−6; R/Ra = 0.66−4.93, averaging 2.53;40Ar/39 Ar ratios vary between 426 and 2073, with the average value of40Ar being 8.32; and the average of4He/40 Ar ratios is 2.17.3He/4He ratios in gneiss and granite in the periphery of the mining district are within the range of 0.001 × 10−6–0.55 × 10−6, reflecting significant differences in their sources.3He and4He fall near the mantle, as is shown in the He concentration diagram. Studies have shown that the ore-forming materials in this region should come from the deep interior of the Earth. With the multi-stage evolution of mantle plume, ore-forming fluids in the deep interior were moving upwards to shallow levels (crust). Under such circumstances, there would be inevitably occur crust/mantle fluid mixing, so their noble gas isotopic characteristics are intermediate between the mantle and the crust.

Tectonic ore-controlling in the middle-southern segment of Da Hinggan Ling, Northeast China

Studies on geotectonic evolution, regionally geological characteristics and ore-forming and ore-controlling structures have shown that since the Mesozoic the Da Hinggan Ling region has entered the typical intercontinental orogenic stage, which appears to be closely related to mantle plume activities. Da Hinggan Ling is a typical mantle branch structure and possesses obvious magmatic-metamorphic complexes in the core, detachment slip beds in the periphery and overlapped fault depression basins. Moreover, all these are the principal factors leading to ore formation and ore controlling in the region. This paper also further explores the mechanism of mineralization in the middle-southern segment of Da Hinggan Ling, summaries the rules of mineralization, puts forward the models of mineralization and points out the ore-search orientations in the future time.

Isotopic Characteristics of Mesozoic Au-Ag Polymetallic Ore Deposits in Northern Hebei and Their Ore-Forming Materials Source*

It has long been a controversy about the source of ore-forming materials of Au-Ag polymetallic deposits both-in metallogenic theory and in ore-searching practice. In terms of a large wealth of the isotopic statistics data from Indosinian-Yanshanian endogenic ore deposits in northern Hebei (generally referring to the areas along the northern part of Taihang Mountains and northern Hebei, the same below), it is considered that the ore-forming materials came from the deep interior of the Earth, which had migrated through plumes to the Earth surface while experienced multi-stage evolution and then emplaced progressively in favorable structural loci to form ores. Their isotope data show that 559 sulfur isotopic data from 40 ore deposits are, for the most part, within the range of −5% - 5%, with a high degree of homogenization, indicating that the sulfur is derived mainly from magma; 200 lead isotope data from 37 ore deposits indicate that the ore-forming materials are principally of mantle source though some crust-source material was involved; 96 oxygen, hydrogen and carbon isotope data from 34 ore deposits illustrate that the ore-forming fluids are dominated by magmatic water while other sources of water would be involved. It may therefore be seen that the formation of endogenic deposits has nothing to do with the strata.