Xuan Liu | Chinese Academy of Sciences (original) (raw)

Papers by Xuan Liu

Dazhuangzi gold deposit lies in Pingdu city, Shandong province, China. Tectonically, it is locate... more Dazhuangzi gold deposit lies in Pingdu city, Shandong province, China. Tectonically, it is located at the southwestern border of Jiaobei terrain, across which is the Mesozoic Jiaolai basin, and to the west, it is adjacent to the Yishu fault zone. The ore bodies, which were hosted in metamorphic rocks of Paleoproterozoic Jingshan Group, can be divided into two types, namely the “altered cataclasite or mylonite type” and “quartz vein type”. Microthermometric investigation reveals that gold precipitation occurred at 240~280℃ from CO2-rich, low salinity (7~8wt.%NaCl) hydrothermal fluids in which there were no other volatiles except H2O and CO2. More importantly, phase separation is recognized and firmly believed to be responsible for the main stage mineralization. Results of hydrogen and oxygen isotope study suggest that ore-forming fluids were a mixture of magmatic water, which might have originated from degassing of mafic magmas deep underneath the region, and meteoric water. Sulfur isotope study demonstrates that sulfides have a δ34S value range of 7.9~11.3‰, which is quite similar to that of metamorphic rocks of Jingshan Group, thus indicating that sulfur in the ore-forming fluids was dominantly derived from the metamorphic rocks of Jingshan Group.

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A large number of daughter mineral-bearing fluid inclusions formed in Q+Py±Cp±Cc veins, phyllic r... more A large number of daughter mineral-bearing fluid inclusions formed in Q+Py±Cp±Cc veins, phyllic rocks and Q+Py+Mo±Cp veins at the Dexing porphyry copper – molybdenum deposit, SE China. On the basis of microscopic investigation of the vein (and rock) mineral assemblages and fluid inclusion petrology, SEM-EDS was employed in identification of the solid phases in fluid inclusions. Our results suggest that 1) transparent daughter minerals in Q+Py±Cp±Cc veins include sericite, halite, bischofite, dolomite, iron-bearing chlorides, apatite and Ce-bearing phosphates, and opaque phases consist of hematite, iron-bearing oxides and chalcopyrite; 2） transparent daughter minerals in phyllic rocks include halite, anhydrite, gypsum, sericite, magnesium sulfate, magnesite, magnesium chloride, (Fe, Cu, Mg) carbonate and sulfate, while opaque phase include hematite, magnetite, rutile and chalcopyrite; and 3) daughter minerals in Q+Py+Mo±Cp veins are far less developed, which include halite, siderite and K-feldspar for the transparent daughters and hematite for the opaque ones. Various types of daughter minerals in Q+Py±Cp±Cc veins, phyllic rocks and Q+Py+Mo±Cp veins indicate that hydrothermal fluids responsible for their formation are significantly complex in composition and appear to be hypersaline, oxidized and ore minerals enriched. However, detailed alteration mineral observation suggests that Na, Ca, Mg, Fe, which appear in those solid phases are probably contributions from the preexisting minerals (plagioclases, hornblendes, biotites and possibly phosphates) by water/rock reaction in the wall rocks. Furthermore, fluid inclusion petrology indicates that those hypersaline fluid inclusions in the phyllic rocks and Q+Py+Mo±Cp veins are likely to be generated from low- or moderate-salinity fluids by fluid-vapor phase separation, which are evidenced by coexistence of daughter mineral-bearing inclusions and vapor-rich inclusions or CO2-rich inclusions. Finally, monazites and Ce-bearing phosphates in the fluid inclusions of Q+Py±Cp±Cc veins suggest that hydrothermal fluids forming these veins are hypersaline, acidic and CO2-bearing. Separation of CO2 from the liquid phases is likely to account for the absence of the Ce from the fluids.

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The Yinshan deposit is a large epithermal-porphyry polymetallic deposit, and the timing and petro... more The Yinshan deposit is a large epithermal-porphyry polymetallic deposit, and the timing and petrogenesis of ore-hosting
porphyries have been hotly debated. We present new results from geochemical, whole-rock Sr–Nd and zircon U–Pb–Hf–O
isotopic investigations. Zircon U–Pb data demonstrate that the quartz porphyry, dacitic porphyry, and quartz dioritic porphyry
formed at ∼172.2 ± 0.4 Ma, ∼171.7 ± 0.5 Ma, and ∼170.9 ± 0.3 Ma, respectively. Inherited zircon cores show signiﬁcant
age spreads from ∼730 to ∼1390 Ma. Geochemically, they are high-K calc-alkaline or shoshonitic rocks with arc-like trace
element patterns. They have similar whole-rock Nd and zircon Hf isotopic compositions, yet an increasing trend in εNd(t) and
εHf(t) values typiﬁes the suite. Older (inherited) zircons of the three porphyries display Hf compositions comparable to those
of the Jiangnan Orogen basement rocks. In situ zircon oxygen isotopic analyses reveal that they have similar oxygen isotopic
compositions, which are close to those of mantle zircons. Moreover, a decreasing trend of δ
18O values is present. We propose
that the ore-related porphyries of the Yinshan deposit were emplaced contemporaneously and derived from partial melting of
Neoproterozoic arc-derived maﬁc (or ultra-maﬁc) rocks. Modelling suggests that the quartz porphyries, dacitic porphyries,
and quartz dioritic porphyries experienced ∼25%, ∼10%, and ∼10% crustal contaminations by Shuangqiaoshan rocks. Our
study provides important constraints on mantle–crust interaction in the genesis of polymetallic mineralization associated
with Mesozoic magmatism in southeastern China.

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The Dexing copper deposit in southeastern China is a typical non-arc porphyry deposit, the origin... more The Dexing copper deposit in southeastern China is a typical non-arc porphyry deposit, the origin of which has
been a topic of debate for several decades. Here we present new results from U–Pb geochronology, whole-rock
chemistry and Sr–Nd–Hf–O isotopic investigations on the ore-forming granodioritic porphyry. LA-ICPMS
zircon U–Pb data suggest that the granodioritic porphyry was formed in the Middle Jurassic (ca. 172.5 Ma)
probably associated with lithospheric thinning driven by either sub-continental lithospheric mantle delami-
nation or asthenospheric upwelling. The porphyry displays both arc-like and adakitic trace element signa-
tures. The adakitic features suggest that HREE (heavy rare earth elements)-rich minerals such as garnet and
hornblende, in the absence of plagioclase resided in the source region. The arc-like signatures are broadly
comparable with those of the proximal Neoproterozoic island arc rocks including the keratophyre from
Shuangxiwu Group and associated granitoids indicating a potential genetic relationship. The porphyry has
chondritic εNd(t) of −0.28 to 0.25 and radiogenic εHf(t) of 2 to 7, and correspondingly, uniform two stage
depleted mantle Nd model ages of 940–980 Ma and Hf model ages of 800–1100 Ma (mean ~920 Ma).
On Nd and Hf isotopic evolution diagrams, these values are markedly similar to those of the adjacent
Neoproterozoic arc rocks when calculated forward to the Mid-Jurassic. Zircons of the porphyry show
mantle-like oxygen isotope characters with δ18O values clustering in the range of 4.7–5.9‰, similar to the
values for the Neoproterozoic arc rocks mentioned above. The geochemical and isotopic features recorded
in our study suggest mantle-derived magmas with no signiﬁcant supracrustal input for the source of the por-
phyry. With regard to the source of the Cu ore, we consider a model involving the remelting of sulﬁde-bearing
arc-related lower crustal source. Furthermore, the occurrence of a Neoproterozoic VMS (volcanic massive
sulﬁde) type copper deposit (the Pingshui Cu deposit) in the Shuangxiwu Group might suggest that the
lower crustal rocks related to a Neoproterozoic relict island arc provided the source for copper during a second
stage melting event. We propose a new geodynamic model for the Dexing porphyry Cu deposit which envis-
ages that the sulﬁde-bearing arc lower crustal rocks were generated during oceanic slab subduction in the
early Neoproterozoic, the remnants of which were preserved at the crust/mantle boundary. Subsequently,
in the Middle Jurassic, these rocks were heated by asthenospheric upwelling and remelted to produce fertile
magmas. The magmas ascended along the Northeast Jiangxi Fault and intruded into the Jiuling terrane where
Cu precipitation occurred upon subsequent magma cooling and ﬂuid exsolution.

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The Dexing porphyry copper and Yinshan polymetallic deposits in Dexing City, southeastern C... more The Dexing porphyry copper and Yinshan
polymetallic deposits in Dexing City, southeastern China are
both giant porphyry ore systems. Located 15 km apart, they
formed synchronously and share a similar magma source and
metallogenic evolution, but their metal endowment, dominant
rock types, and alteration assemblages differ significantly. In
this contribution, we investigate the cause of these distinctions
through new molybdenite Re–Os ages and zircon and apatite
(U–Th)/He thermochronology data. Dexing has a molybde-
nite Re–Os age of ~170.3 Ma, zircon (U–Th)/He (ZHe) ages
of 110 to 120 Ma and apatite (U–Th)/He (AHe) ages of 7 to
9 Ma. In contrast, Yinshan has older ZHe ages of 128 to
140 Ma and an AHe age of ~30 Ma. Viewed in combination
with previously published data, we conclude that the appar-
ently slow cooling experienced by these bodies is primarily a
reflection of their experiencing multiple episodes of thermal
disturbance. We tentatively infer that both deposits were ex-
posed in the Late Miocene or more recent time, with the
Dexing deposit more deeply exhumed than Yinshan. Our
study has exploration implications for deeper porphyry-style
ores at Yinshan and for porphyry deposits in non-arc
(intraplate) settings in general.

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