High heat production of the Late Mesozoic Luanchuan granites from East Qinling Orogen, China: Implications for petrogenesis and mineral exploration

Some of the high heat production granites in the continental crust have been suggested to be linked with I-, A-, and partly S-type granitoids which aided in the formation of associated polymetallic deposits. Here, we investigate the Shibaogou and Laojunshan plutons in the Luanchuan region, East Qinling Orogen, China, and integrate these with published geochemical information to compute the rate of heat production per unit rock mass (RHP value, unit mu W/m(3)). In addition, we also present RHP contour maps of all the Late Mesozoic granitic plutons in the Luanchuan region, with a view to evaluate the link among the high heat production granites, their petrogenesis and mineralization. The RHP values of granitoids in the Luanchuan region vary from 1.7 to 14.44, with the Nannihu pluton showing the highest RHP peak value of 6.04, whereas the Huoshenmiao pluton has the lowest RHP peak value of 2.59. The RHP values have a positive correlation with the degree of magma differentiation, as suggested that the Nannihu pluton is a highly fractionated I-type granite and the Huoshenmiao pluton is a quartz diorite. This is also consistent with U, Th and K which are incompatible elements that tend to enter the melt during magma evolution. Furthermore, the higher RHP value intrusions (e.g., Nannihu, Daping) show close genetic links with high economic deposits, whilst the plutons with lower RHP values are generally related to small ore deposits. We envisage that the high heat production granites underwent protracted cooling process, which promote the convection and circulation of hydrothermal fluids, so that ore-forming materials (e.g., Mo, W) can sufficiently accumulate and precipitate as economic mineralization. This also indicates that these granitoids with relatively higher RHP values have a greater metallogenic potential. The RHP contour mapping results show high RHP value domains ranging from 2.68 to 4.82 in the southeast and northeast segments of the Shibaogou pluton, whereas the RHP values of other regions in this pluton vary from 2.14 to 2.68. In contrast, the high RHP value regions mostly occur within the western and eastern parts of the Laojunshan pluton, and range from 4.91 to 6.21. Other regions in the Laojunshan pluton have low RHP values in the range of 2.69-4.91. A few Mo-W deposits are mostly hosted in the southeastern part of the Shibaogou pluton, implying that these regions with high RHP values might have higher metallogenic potential. The contour mapping of RHP maximum, minimum, average and peak values of all the Mesozoic granitic plutons in the Luanchuan region also show high value zones within and/or at peripheral regions of the Nannihu ore fields and these segments between the Nannihu and Yuku ore fields, which suggest that these zones likely have high potential for Mo-W exploration.