Abstract
The Longquanzhan deposit is one of the largest gold deposits in the Yi-Shu fault zone (central section of the Tan-Lu fault zone) in Shandong Province, China. It is an altered-rock type gold deposit in which ore bodies mainly occur at the contact zone between the overlying Cretaceous rocks and the underlying Neoarchean gneissic monzogranite. Shi et al. reported that this deposit formed at 96 ± 2 Ma using pyrite Rb–Sr dating method and represents a new gold mineralization event in the Shandong Province in 2014. In this paper, we present new He–Ar–S isotopic compositions to further decipher the sources of fluids responsible for the Longquanzhan gold mineralization. The results show that the δ34S values of pyrites vary between 0.9‰ and 4.4‰ with an average of 2.3‰. Inclusion-trapped fluids in ore sulfides have 3He/4He and 40Ar/36Ar ratios of 0.14–0.78 Ra and 482–1811, respectively. These isotopic data indicate that the ore fluids are derived from a magmatic source, which is dominated by crustal components with minor mantle contribution. Air-saturated water may be also involved in the hydrothermal system during the magmatic fluids ascending or at the shallow deposit site. We suggest that the crust-mantle mixing signature of the Longquanzhan gold deposit is genetically related to the Late Cretaceous lithospheric thinning along the Tan-Lu fault zone, which triggers constantly uplifting of the asthenosphere surface and persistent ascending of the isotherm plane to form the gold mineralization-related crustal level magma sources. This genetic model can be applied, to some extent, to explain the ore genesis of other deposits near or within the Tan-Lu fault belt.
Highlights
The Shandong Province situated in the southeastern margin of the North China Craton (NCC) is the largest gold-producing region in China
A variety of studies has been conducted on these gold deposits over the past decades and have revealed that gold metallogeny across the Shandong Province contrasts markedly, i.e., by mineralization type, mineralization age, and mantle dynamics (EMII type vs. EMI type, [1,5,6])
The new data are combined with noble gas obtained for the Yi’nan and Qibaoshan gold deposits (Figure 1) and previously published isotopic data for other gold deposits in the Luxi and Jiaodong in order to discuss gold mineralization variations across the Shandong Province
Summary
The Shandong Province situated in the southeastern margin of the North China Craton (NCC) is the largest gold-producing region in China It has proven reserves exceeding 5000 tons (t) Au and more than 150 active gold mines produce at least 30 t of gold per year [1,2,3]. Few studies have been conducted comparing the Longquanzhan deposit with other gold deposits across the Yi-Shu fault zone (i.e., from the Luxi to the Jiaodong). Noble gas and sulfur isotopes of pyrites in the main gold mineralization stage are measured to trace the sources of ore-forming fluids and metals for the Longquanzhan deposit and to further constrain the origin of Late Cretaceous gold mineralization event in the Yi-Shu fault zone. The new data are combined with noble gas obtained for the Yi’nan and Qibaoshan gold deposits (Figure 1) and previously published isotopic data for other gold deposits in the Luxi and Jiaodong in order to discuss gold mineralization variations across the Shandong Province
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