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Tourmaline is common in magmatic-hydrothermal deposits, and its composition and boron isotope geochemistry have been widely used to fingerprint the source and evolution of hydrothermal fluids and associated metals. However, whether these chemical or boron isotopic compositions or their combinations can be used as vectors for mineral exploration remains to be explored. In this study, we documented the major and trace element compositions and boron isotopic values of tourmaline along a vertical extension (i.e., 510, 830, 1230 m above sea level, a.s.l.) of the newly discovered porphyry Au mineralization in the Hewan feldspar quartz porphyry, Yixingzhai deposit, to shed light on the evolution of the ore-forming fluid, the mechanisms of Au deposition, and potential indicators for Au exploration. Field observations showed that tourmaline in the Hewan porphyry occurred mainly as orbicules or veins and intergrew with Au-bearing pyrite, hydrothermal quartz, and some clay minerals, indicating a magmatic-hydrothermal origin. Tourmaline sampled from 510 m a.s.l. showed δ11B values (–11.5 to –9.3‰) consistent with those of the average continental crust and tourmaline in magmatic systems, which suggests that the ore-forming fluid was most likely exsolved from the host Hewan porphyry. The δ11B values became heavier upward, reaching –9.9 to –1.5‰ at 830 m and –8.0 to +6.8‰ at 1230 m a.s.l. This boron isotopic variation, integrated with increasing Fe, Mg, Na, Ca, Li, Co, and Sr but decreasing Al, U, Th, REE, Zn, and Pb contents of the tourmaline samples from deep to shallow levels, implies that the initial magmatic fluids were gradually mixed with circulating meteoric water that contained materials leached from peripheral Archean metamorphic rocks and Mesoproterozoic marine sedimentary rocks. Considering the spatial distribution of the Au grade of the porphyry, we propose that a suitable mixing proportion of magmatic and meteoric fluids caused Au deposition and accumulation. We note that tourmaline samples collected from the economic Au zones had much lower and more concentrated δ11B (–11.5 to –3.0‰), Co/(Pb+Zn) (<0.01), and Sr/ (Pb+Zn) (0.27 to 1.07) values than those in low-grade or barren zones. Coeval plutons and breccia pipes, where tourmaline also occurs, are well developed inside and outside the Yixingzhai Au mine. We suggest that the obtained parameters can potentially be used as proxies for further Au exploration in this region. This study highlights the feasibility of using the chemical and isotopic compositions of tourmaline for mineral exploration. [ABSTRACT FROM AUTHOR]

Halogens (Cl, Br, and I) are major complexing agents for metal ions, and their ratios (Br/Cl and I/Cl) have been used to determine the source and evolution of hydrothermal fluid. Halogen fractionation during hydrothermal fluid evolution, however, has been inferred from several studies, which poses problems in using halogen ratios as a fluid tracer. The Br/Cl and I/Cl ratios of scapolite are consistent with those ratios present in the coexisting fluid during scapolite formation, making this mineral particularly useful for understanding hydrothermal fluid evolution. To better understand halogen fractionation during vapor-brine phase separation, we conducted fluid inclusion microthermometry, major elements, and in situ halogens and Sr isotope analysis of scapolite formed from a high-salinity hydrothermal fluid during the vapor-brine phase separation at the Yixingzhai gold deposit, North China Craton. The studied scapolite has 1.84–3.41 wt% Cl, 389–806 ppm Br, 8.4–24.4 ppm I, and significantly high Br/Cl (6.1–14.7 × 10–3) and high I/Cl (91–302 × 10–6) molar ratios that likely result from the preferential incorporation of Br and I into the brine phase compared to Cl entering the vapor phase during fluid phase separation. Based on fluid inclusion microthermometry results, the Rayleigh fractionation simulation shows that the Br/Cl and I/Cl ratios of the brine are estimated to be up to 18 × 10–3 and 500 × 10–6 during the formation of scapolite. These results reveal halogen fractionation during the vapor-brine phase separation of hydrothermal fluids. This view has implications for interpreting the halogen systematics of scapolite and other minerals formed in similar environments, particularly when they are used as a fluid tracer. [ABSTRACT FROM AUTHOR]

We assessed the problem of low mixing efficiency caused by unstable signal polarization because of a moving reflector in a laser communication terminal with a periscopic scanner. A real-time polarization compensation method based on rotating waveplates is presented, which keeps the receiving signal light polarization at 45° linear polarized and improves system mixing efficiency. A geometric model of the laser communication terminal was first established, its polarization transmission characteristics were analyzed by three-dimensional polarization tracks, and a system polarization transmission matrix was calculated. The relationship between scan angle and polarization of the output signal was simulated. The connections between a polarization-compensating λ/4 waveplate and the λ/2 waveplate rotation angle and scan angle were established. These findings will pave the way for real-time polarization control technology for coherent free-space laser communications.