The Research And Significance Of Alteration Zones And Geochemical Characteristics In Open-pit Area At Zijinshan Gold Mine

Zijinshan orefield is an important polymetallic mineralization district of Wuyi metallogenic belt with the relationship to Mesozoic tectonic-magmatic activity. Yueyang low-sulfur epithermal silver polymetallic deposit, Zijinshan high-sulfur epithermal gold-copper deposit, Luoboling porphyry copper-molybdenum deposit and lots of transitional copper deposits forms an epithermal-porphyry polymetallic mineralization system. Among them, Zijinshan gold-copper deposit is the most important and the largest high-sulfur epithermal gold-copper deposit in china.Many researchers have already made lots of researches on mineral deposit geology, petrology, geochemistry, mineralogy and metallogenic epoch, they have got lots of achievements, but they have paid little attention on strong rock alteration and its feature, and also paid little attention on geochemical feature of alterated rock and mineral ore. In this paper, we use portable infrared mineral analysis (PIMA) technology to identify the alterated mineral component and divide the alteration zones, then make comprehensive analysis on major elements, trace elements and rare elements in alterated rock and mineral ore. Compared with the researches of metallogenic fluid and isotope geochemistry, we make the following main results and achievements:1. The paper preliminarily divides five alteration zones in open-pit area, they are Quartz+Micasericite (Q+Ms) alteration zone, Quartz+Dickite (Q+Di) alteration zone, Quartz+Alunite (Q+Alu) alteration zone, Quartz+Dickite+Micasericite (Q+Di+Ms) alteration zone and Quartz (Q) alteration zone, the distribution of Q alteration zone may be consistent with gold mine and the distribution of Q+Alu alteration zone may be consistent with concealed copper mine.2. The feature of major elements shows that the contents of SiO2 and Fe2O3 are higher in mineral ore and alterated rock than in granite pluton, the content of Al2O3, MnO, MgO, CaO, Na2O and K2O are lower in mineral ore and alterated rock than in granite pluton. The hign content component (SiO2, Fe2O3) impossibly came from alterated rock, but from mineralizing fluid. It’s possible that multi-stage alteration was closely related to mineralization.3. The feature of rare elements shows that the content of total REE in alterated granite and mineral ore is much low but rich in LREE, LREE and HREE shows weak internal variation which displays negative Eu anomalies; The figure of REE patterns is a slight right "V" type which displays clear negative Eu anomalies. Alterated dacite-porphyrite shows strong internal variation and weak negative Eu anomalies, crystal separation during the formation of rock was not obvious, granite and dacite-porphyrite were product of different magma sources.4. The feature of trace elements shows that Rb, Th, U, K, Nb, Yb are rich but Ba, Sr, P, Ti are relatively less in granite pluton. The spider diagrams of alterated rock and mineral ore show similar feature, Th, U, Nb, Yb are rich but Ba, Sr, P, Ti, Yb are less, granite pluton may come from crustal material by partial melting with the characteristics of multi-stage in mineralization. Au, Cu and Ag should belong to the same middle-low epithermal combination of elements and some minerals may come from deep earth, Mo should belong to another metallogenic system.