Geochemical characteristics of ferrif-erous silicalites in the Zheyaoshan deposit of the Baiyinchang copper polymetallic orefield in Gansu Province and their ore-prospecting significance

The ferriferous silicalites in the Zheyaoshan ore district occur in sedimentary discontinuity interface between the ore-bear-ing rock series (quartz keratophyre taff) and the upper rock system, and are composed mainly of fine-crystalline quartz and hematite, which account for more than 90%, with a small amount of silk mica, feldspar, sodium chlorite etc. The ferriferous silicalites are charac-terized by low TiO2 and A12O3 as well as high ore-forming elements (Fe, Cu, Pb, Zn). Through the calculation of Al/(Al+Fe+Mn) ratio, the characteristics of hydrothermal sedimentary rock were displayed. In the Fe-Mn-Al triangular diagram, Fe-Mn-(Cu+Co+Ni)×10 triangular diagram and Zr-Cr diagram, the ferriferous silicalites in this area are located in the hydrothermal sedimentary rock area, the total REE of ferriferous silicalites is very low, and the north American shale standardization distribution pattern is a right-oblique curve with weak negative Eu anomaly or positive Eu anomaly as well as weak negative Ce anomaly. The ω(MnO)/ω(TiO2) ratio of part of the samples is somewhat smaller, U/Th ratio is larger, Al2O3 content is higher, with a negative Eu anomaly, in-dicating that the addition of normal sedimentary silicalite ingredients. Combined with the geological background of ferriferous sili-calites and rare earth elements of ore-bearing rock series (quartz keratophyre tuff) and mineralized quartz, the authors hold that the provenance of ferriferous silicalites was mainly derived from quartz keratophyre tuff and belonged to the abiogenic type related to vol-canism, and this can be regarded as an important prospecting criterion in the orefield.