Y. Cao’s scientific contributions

Gold Mineralization of the Shihu deposit can be divided into 4 stages, pyrite-quartz stage, quartz-pyrite stage, polymetallic sulfide stage and quartz-carbonate stage. Cell parameters of pyrite and quartz from 4 stages were analyzed in this paper. The analytical results of pyrite indicated that the value of &Q and uo is minimum in UJ stage; the values of a- and u0 decrease as mineralization stage proceeds from I to IV and as the depth of ore-body increases from 560 to 180 meters. The analytical results of quartz indicated that the values of co and the Co/ao, ratios decrease as mineralization stage changes; the values of ao increase as the depth of ore-body increases; the values of Co and the C o/ao, ratios change rhythmically as the depth of ore-body increases. Results of cell parameters suggested that pyrites have high contents of Co, Ni and As, and have not undergone S depletion. Moreover, Al and Fe are the major replacement impurities in isomorphism of quartz. Gold-bearing pyrites are characterized by small ao , while gold-bearing quartz are characterized by big ao, small Co, and C o/ao ratio. The values of ao, of pyrite and the values of Co and Co/ao ratios of quartz are mostly larger than their ideal values. Therefore, denudation of the gold ore-body is slight, and potential value of this deposit is considerable.

Rare earth elements of single zircon from Mesozoic magmatic rocks in north Taihang Mountain were analyzed by LA-ICP MS. The result reflect that average values of ∑REE, δEu and (Lu/Gd)N of the zircons from granite and granodiorite were 747. 08×10-6 and 704.84×10-6, 0.47 and 0.49, 23.55 and 24.12 respectively. A strong consistency of the zircons rare earth characteristics indicated that the central face was coincident with marginal face of the rock body, their two faces could originate from the same magma source. However, average values of ∑REE, δEu and (Lu/Gd)N of the zircons from the diorite and quartz diorite porphyrite were 989. 69×10-6 and 560.00×10-6, 0.56 and 0.75, 20.59 as well as 17.49 respectively. The obvious differences of the zircons rare earth characteristics indicate that the two kinds of dikes can originate from the different magma source triggered by different formation mechanism. The results showed that the (Lu/Gd)N and δEn were two important parameters which were relativley stable but some ratios of the rare element related with La (or ∑LREE) eg. ∑HREE/∑LREE and (Sm/La)N were unstable in determining the characteristics of zircon as ∑LREE especially La usually changed in a lager scope. Combining the results above with isotopic dating resulted and CL imaged, the geodynamic ground of this region was consistent with super-large gold deposit in eastern Shandong, which was large-scale lithosphere thinning of North China Craton and interaction of crust and mantle. The higher fO2 of gold-bearing deep fluid (transmagmatic fluids) carried by quartz diorite porphyrite that originate from the deepest mix with lower f02 of post-magmatic hydrothermal and underground water, and at last resulted in the formation of gold veins in the fracture of genesis as host rocks.

This paper introduces the application of the pyrite thermoelectric property measurements in gold exploration of the Shihu gold deposit. Pyrite is the main gold-carrying mineral. Four gold mineralization stages may be distinguished. The thermoelectric type assemblage of pyrite is P<N⇒P≥N⇒P>N⇒P≤N from mineralization stages I to IV. In the mineralization area, from the top downward when (P and P% decrease, (N and N% increase, which in the main coincides with the results of mineralogical mapping by using the distribution of pyrite type (P%) and the mean of the thermoelectric coefficient (P. Some typomorphic information such as formation temperatures of pyrite, relative burial depths of orebodies, characteristics of orebodies and prospects of the deep part may be obtained according to thermoelectric properties of pyrite.

The authors discuss the ore-forming temperatures, orebody size and mineralization stages of the Qianhe gold deposit by using the thermoelectricity and decrepitation temperatures of pyrite from the deposit and evaluate the ore prospects at depths in the ore district by using mineralogical mapping. The study results show that the ore-forming temperatures of the deposit range from 222.3 to 360.1°C, indicating that the deposit is a mesothermal one. The thermoelectric properties of pyrite in all the levels are of the N type, with the total content reaching 81.4%. Spatially, the degree of erosion of the orebody shows the rhythmic feature, i.e. being from high to low and again to high, which indicates that the gold orebody is persistent form the 200 to 520 m levels and has a tendency to continue downward. There are mainly three types of decrepitation peak for pyrite, which correspond to the early, middle and late mineralization stages respectively.

The Qianhe gold deposit, Henan, is of tectonic alteration type. In this deposit, orebodies show gradational contact relationships with wall rocks with a vague boundary, but there is distinct difference in magnetic susceptibility among orebodies, wall rocks and various types of altered rocks. Systematic susceptibility measurements were made of altered rocks in various levels and along exploratory lines of the Qianhe gold deposit using a WCL-1 portable contact magnetic susceptibility meter. The susceptibility values of various kinds of typical altered rocks are in decreasing order as follows: chloritized rocks (Ch) → silicified-chloritized rocks (Si+ Ch) → chloritized-silicified rocks (Ch+Si) → K-feldspathized rocks (Kf) → silicified (Si) → pyritized-phyllic rocks (Py+Se+Si). Correlation analysis of the magnetic susceptibilities of altered rocks and degrees of gold mineralization indicates that there is a negative correlation trend between them. Profiles of magnetic susceptibilities of altered andesite along lines 78 and 83 and a vertical longitudinal projection map of magnetic susceptibilities and gold grade isolines in the ore district have been constructed, and the direction for looking for ore deposits at depth in the ore district has been predicted preliminarily.