The Xinping Dahongshan - The Yuanjiang Summarized Division Copper And Iron Metal Metallogenic Series And Metallogenic Prediction

The doctoral dissertation, The Iron and Copper Poly-metal Metallogenic Series and Minerogenetic Targeting of Xinping Dahongshan-Yuanjiang Cuoke Area, is based on the scientific research requirements for the project, Assessment of the Copper and Iron Minerals in Yuanjiang Cuoke-Xinping Dahongshan Area, Yunnan, a sub-project of The Base Survey for Non-ferrous Metal at Yunnan Section of the Southwest Three Rivers sponsored the Ministry of Land and Resources, P.R.C.In this paper, an approach combining metallogenic series theory with comprehensive information minerogenetic prognosis method is adopted, and based on the widely collected data including geological mineral, geophysical and geochemistry prospecting, remote sensing, scientific research, survey and the result and knowledge of predecessors and a large amount of field observation and research, three large metallogenic series (or sub-series) have been collated and stipulated. In the first metallogenic series—the iron, copper and gold metallogenic series relevant to albite-rich volcano-volcanic sedimentary function of early Proterozoic, Dahongshan-type iron and copper ore deposit, a typical mineral deposit, is selected as the important dissection object. Comprehensive geological studies have been conducted on ore-bearing potential, petrology and the tectonic environment of the metamorphic volcanic rock formation. Other research work includes the systematic studies on deposit, irrespectively geologic of deposit, geochemical features and on the microelements, REE, geochemical characteristics of the isotopes, fluid inclusions and minerogenetic regularities, etc. On the basis of the detailed studies of the minerogenetic geological background, geophysical and geochemical characteristics and remote sense image, with the computer and high-tech technology (i.e. GIS), metallogenic prognosis researches of comprehensive information has been conducted on the iron and copper poly-metal minerogenetic belt of Xinping Dahongshan-Yuanjian Cuoke, the following important results have been achieved:1. The evolution of geological tectonics and its control over minerogenesis in this research region are established. The minerogenetic belt of Kang-Dian Axis in the study area has gone through a very long evolution history, and the polycyclic rifting in the region has brought about minerogenetic polycycle, thus forming varieties of minerals. Dahongshan-type copper and iron ore deposit is formed in the nascent aulacogen of the continental margin. The rifting has resulted in the marine basin with relative closing, which is closely related to the formation of the deposits. At the deep valley of the basin, with the surging effect of the materials of upper mantle magma column from the paleo-land core, volcanic activities have broken out in aulacogen. Dahongshan copper-iron ore deposit of the volcanic rock type is formed in such albite-rich lava and tuffs constructed by the spilitic keratophyre-terrigenous clastic sedimentary-carbonate formation, both of which are mid-ocean ridge basalt with exclusive copper-iron minerogenetic property.2. The metallogenic series in the study area have been collated and stipulated. These metallogenic series can approximately be arrayed in accordance with chronologically evolved order as iron, copper and gold metallogenic series relevant to early Proterozoic albite-rich volcanic sedimentary formation, copper, iron and REE metallogenic series relevant to early Mesoproterozoic sedimentary-reconstructing transition, and sedimentary-reconstructing copper deposit metallogenic series of the glutenite in late Mesozoic Erathem. These overall series reveal the types of the deposits, ore-controlled regulations and prospecting orientation. The typical cases of the three metallogenic series are considered, Dahongshan type, Cuoke type, Luoxue type, Yimen type and sedimentary-reconstruct copper deposit type of Late Triassic Series in sand and conglomerate are partitioned, and the typical ore deposits are dissected, which provides empirical study for each metallogenic series.3. The petrology and geochemistry characteristics of Dahongshan iron-copper are disclosed in the paper. The petrochemical study shows that the iron-copper deposit is closely related to albite-rich volcanic rocks. The ore-bearing wallrock, ore body and sub-volcanic rock have near or same formation conditions and environments, and the ore deposit is a metallogenic series of alkalescent basic volcanic rock relevant to the eruption action of submarine volcano. The statistical analysis of the microelements reveals that the microelement combination of ores is nearly the same as that of wallrock, which shows that both of them have the same material source. The distribution pattern of the REE embodies the steep tilting curve of LREE enrichment and negative anomaly of Eu, which shows alternation and metamorphism have strongly reconstructed the plagioclase of the original rock, and Ce is generally weak negative anomaly. (La/Sm)>1, and the rock has the characteristics of mid-ocean ridge T-type basalt. The gross amount of REE is relatively small and LREE is obviously rich in the rocks, which belong to the LREE enrichment type.4. The minerogenetic temperature, the matter source, the ore-forming fluids and the minerogenetic epoch of Dahongshan type iron-copper deposit have been systematically studied. The uniform temperature of inclusions is between 102℃and 370℃, which shows there exist two stages of mineralization: the early minerogenetic stage has 290-330℃uniform temperature, 16-32wt% salinity, the pH value of 3.7-3.0, logfs₂-70.2, logfo₂-26.55 and logfco₂ 3.3-1.5; while the late minerogenetic stage has 160-250℃uniform temperature 13.8-45wt% salinity, the pH value of 4.5-3.4, logfs₂-11.04, logfo₂-34.37 and logfco₂ 4.63-3.9. This shows the formation temperature is evolved from intermediate temperature(290-330℃) to intermediate-low temperature with the stage going from early to late. The isotope analysis of lead reveals that the mixed lead is originated from different sources, environments and stages. The isotope analysis of sulfur shows that the sulfur is originated from the reduction of sulfate of the sea water and part of which is originated from mantle sulfur carried up from deep part by volcanic eruption. That is to say, the sulfur is originated from the sulfur formed in volcanic activities mixed with that reduced from sea water; Judged from the value of d ¹⁸O_H2O and dD_H2O, the origin of the minerogenetic liquid (i.e. water) is relatively complex, and the media water of the minerogenetic period of the volcanic sedimentary is mainly originated from original magmatic water. Affected by sea water to a certain extent, during the reconstruction of late regional metamorphism, the minerogenetic liquid gradually evolved into minerogenetic fluid of magmatic water, metamorphic water combined with atmospheric condensation water. The chronological studies of isotopes shows that the age of K/Ar isotopes is mainly near 800Ma±20 Ma and this reveals the late alteration and reconstruction events of copper and iron mineral deposit of Dahongshan type and represents the era when volcanism, metamorphism and mineralization of uranium happened during Jinningian period. And the age is also the reconstruction age of Dahongshan ore deposit.5. The metallogenic series theory is applied to guide the prediction of ore finding. The 5 ore-controlled factors and 8 minerogenetic prediction signs of ore finding in the Dahongshan group is summarized according to the distribution regularity of the ore deposit in space expatiated by the metallogenic series and the regularity of evolution in epoch, which establishes the theory base on comprehensive information minerogenetic prediction.6. The geological, geophysical-geochemical characteristics of Dahongshan type iron-copper ore deposit are mainly researched on and the minerogenetic model for this ore deposit is established. Multivariate minerogenetic information theory is applied to discuss the overall geological characteristics in the researched area, including minerogenetic geological background, geochemistry, geophysics and remote sensing, and the geophysical and geochemical exploration models of ore finding and exploration at the Dahongshan type copper-iron ore deposits in the researched area are generally summed up. This paper also uses GIS-based multivariate physiographical minerogenetic information to carry out target area locating prediction for Dahongshan and Kunyang group in early Proterozoic. Finally, the research points out the prospect area of ore-finding and indicates the orientation for the ore-finding exploration of mines.