Search

Thermoelectric effects are one of the promising ways to utilize waste heat. Novel approaches have appeared in recent decades aiming to enhance thermoelectric conversion. The theory of energy filtering of free carriers by inclusions is among the latest developed methods. Although the basic idea is clear, experimental evidence of this phenomenon is rare. Based on this concept, we searched suitable systems with stable structures showing energy filtering. Here, we report on the anomalous behavior of Cr-doped single-crystal Bi2Se3 that indicates energy filtering. The solubility of chromium in Bi2Se3 was studied, which is the key parameter in the formation process of inclusions. We present recent results on the effect of Cr-doping on the transport coefficients on a wide set of single crystalline samples. Magnetic measurements were used to corroborate the conclusions drawn from the transport and X-ray measurements., Termoelektrické jevy jsou jednou ze slibných cest k zužitkování odpadního tepla. V posledních dekádách se objevily nové přístupy s cílem zlepšení termoelektrické konverze. Teorie energetického filtrování volných nositelů inkluzemi náleží mezi poslední rozvinuté metody. Ačkoliv je základní idea jasná, experimentální pozorování tohoto fenoménu je řídké. S ohledem na tento koncept jsme tak hledali vhodné systémy se stabilními strukturami, které by vykazovaly energetické filtrování. V článku pojednáváme o anomálním chování monokrystalu Bi2Se3 dopovaného Cr, který naznačuje energetické filtrování. Byla studována rozpustnost chromu v Bi2Se3, která je klíčovým parametrem v procesu tvorby inkluzí. Prezentujeme nové výsledky vlivu dopování Cr na transportní koeficienty na široké sérii monokrystalických vzorků. Magnetických měření bylo užito k podpoře výsledků koncipovaných na základě transportních a RTG měření.

The deposit is located in the transitional belt between the Yangtze platform and the Xiongpan-Ganzi folded belt. It lies in the convergence of the Indian, Eurasian and Pacific plates. Strata in the area are low grade metamorphic rocks including marbles, slates and schists, with the main wall-rocks of the tellurium ore veins being schist and slate. The ores grade 0.01-34.58% Te, mostly in tetradymite, found with pyrite, pyrrhotite, dolomite and quartz. On the basis of geological and geochemical characteristics it is concluded that the ore-forming elements were mainly derived from the mantle, with the main mineralisation process being the forming of tellurium ore magma at depth., The deposit is located in the transitional belt between the Yangtze platform and the Xiongpan-Ganzi folded belt. It lies in the convergence of the Indian, Eurasian and Pacific plates. Strata in the area are low grade metamorphic rocks including marbles, slates and schists, with the main wall-rocks of the tellurium ore veins being schist and slate. The ores grade 0.01-34.58% Te, mostly in tetradymite, found with pyrite, pyrrhotite, dolomite and quartz. On the basis of geological and geochemical characteristics it is concluded that the ore-forming elements were mainly derived from the mantle, with the main mineralisation process being the forming of tellurium ore magma at depth.

The large Portovelo-Zaruma gold field is associated with Early Miocene continental arc magmatism. Quartz-sulphide veins crosscut andesitic lavas and tuffs. Pyrite, chalcopyrite, sphalerite and galena are the dominant ore minerals (5-10 vol%). Au occurs in visible and submicroscopic forms, mainly in chalcopyrite (up to 421 g/t). Petzite, hessite and tetradymite were identified in druse quartz in assemblages with native Au. There are large variations in the composition of petzite, from Ag3AuTe2 to Ag3Au(Te1.31S0.61). The hessite contains 1.56-5.23 wt% Au, 0.15-0.46 wt% Fe, 0.0-0.93 wt% Pb and 0.0-0.48 wt% Bi. The tetradymite composition varies from Bil.9Te2S to Bi2Te1.9(S0.6Se0.44). Fluid inclusion homogenisation temperatures range from 134 to 331 degrees C. Salinities are in the range 9.3-0.2 wt.% (NaCl equivalent) corresponding to shallow subsurface conditions. Isotope data suggest a magmatic source for the sulphur in fluids., The large Portovelo-Zaruma gold field is associated with Early Miocene continental arc magmatism. Quartz-sulphide veins crosscut andesitic lavas and tuffs. Pyrite, chalcopyrite, sphalerite and galena are the dominant ore minerals (5-10 vol%). Au occurs in visible and submicroscopic forms, mainly in chalcopyrite (up to 421 g/t). Petzite, hessite and tetradymite were identified in druse quartz in assemblages with native Au. There are large variations in the composition of petzite, from Ag3AuTe2 to Ag3Au(Te1.31S0.61). The hessite contains 1.56-5.23 wt% Au, 0.15-0.46 wt% Fe, 0.0-0.93 wt% Pb and 0.0-0.48 wt% Bi. The tetradymite composition varies from Bil.9Te2S to Bi2Te1.9(S0.6Se0.44). Fluid inclusion homogenisation temperatures range from 134 to 331 degrees C. Salinities are in the range 9.3-0.2 wt.% (NaCl equivalent) corresponding to shallow subsurface conditions. Isotope data suggest a magmatic source for the sulphur in fluids.

Trace elements can be alloyed with gold or form mineral intergrowths or microscopic inclusions. Electron microprobe analysis of over 8 000 sectioned grains from around the world detected, in order of frequency, Ag, Hg, Cu, Pd, Pt, Sb and Fe; rarely, native gold was intergrown with Au-rich compounds such as Au3Cu or native metals such as Bi. Most elements occurred as inclusions less than 5 micrometres in diameter, detected in 20% of gold grains, usually in small numbers (1-10/grain) but occasionally forming over 30% of the section area. Up to 6 different opaque inclusions have been found in one grain, either singly or in clusters; a total of over 90 opaque minerals and over 20 non-opaque minerals have been found as inclusions. Their identities in alluvial gold are a good guide to the type of source mineralisation. The most common inclusions are of pyrite, arsenopyrite, galena, chalcopyrite, pyrrhotite, gersdorffite (NiAsS), hessite (Ag2Te) and tetradymite (Bi14Te13S8), but other elements include Zn, Cd, Sn, Mo, Co, Hg, Pd, Pt, Sb and Se., Trace elements can be alloyed with gold or form mineral intergrowths or microscopic inclusions. Electron microprobe analysis of over 8 000 sectioned grains from around the world detected, in order of frequency, Ag, Hg, Cu, Pd, Pt, Sb and Fe; rarely, native gold was intergrown with Au-rich compounds such as Au3Cu or native metals such as Bi. Most elements occurred as inclusions less than 5 micrometres in diameter, detected in 20% of gold grains, usually in small numbers (1-10/grain) but occasionally forming over 30% of the section area. Up to 6 different opaque inclusions have been found in one grain, either singly or in clusters; a total of over 90 opaque minerals and over 20 non-opaque minerals have been found as inclusions. Their identities in alluvial gold are a good guide to the type of source mineralisation. The most common inclusions are of pyrite, arsenopyrite, galena, chalcopyrite, pyrrhotite, gersdorffite (NiAsS), hessite (Ag2Te) and tetradymite (Bi14Te13S8), but other elements include Zn, Cd, Sn, Mo, Co, Hg, Pd, Pt, Sb and Se.

Among the widespread skarn mineralisation in the Taebaeksan basin, hosted by Palaeozoic calcareous units intruded by Cretaceous granitoids, an extensive alteration zone in the area of the Geodo mine has locally developed ore mineralisation of Fe-oxide, Cu-rich and Au-rich types. Although only Fe and Cu were previously mined, the composition of associated intrusions and chemistry of skarn garnet and clinopyroxene resemble those of Au skarns elsewhere and a small minable gold resource of 53 700 tonnes averaging 1.2 g/t Au and 63.9 g/t Ag has been identified by recent drilling. Au in retrograde alteration of a garnet-rich proximal skarn is closely related to Bi- and Te-rich bismuthinite and tetradymite, suggesting with low-temperature fluid inclusions and chlorite geothermometry that it was deposited late in the evolution of the mineralising system, liquid Bi having possibly acted as a collector. The study results indicate that extensive, apparently barren skarns may host mineralisation in specific areas of the calc-silicate alteration zone and that past production does not preclude the potential for previously unrecognised ore zones., Among the widespread skarn mineralisation in the Taebaeksan basin, hosted by Palaeozoic calcareous units intruded by Cretaceous granitoids, an extensive alteration zone in the area of the Geodo mine has locally developed ore mineralisation of Fe-oxide, Cu-rich and Au-rich types. Although only Fe and Cu were previously mined, the composition of associated intrusions and chemistry of skarn garnet and clinopyroxene resemble those of Au skarns elsewhere and a small minable gold resource of 53 700 tonnes averaging 1.2 g/t Au and 63.9 g/t Ag has been identified by recent drilling. Au in retrograde alteration of a garnet-rich proximal skarn is closely related to Bi- and Te-rich bismuthinite and tetradymite, suggesting with low-temperature fluid inclusions and chlorite geothermometry that it was deposited late in the evolution of the mineralising system, liquid Bi having possibly acted as a collector. The study results indicate that extensive, apparently barren skarns may host mineralisation in specific areas of the calc-silicate alteration zone and that past production does not preclude the potential for previously unrecognised ore zones.

The NE-trending fault cuts biotite granite and K-feldspar porphyroblastic granodiorite. Along its 8 km are four medium-sized deposits, Jiehe, Shangzhuang, Hedong and Fujia, in altered rocks of the fault shatter zone. Ore microscopy has shown that native gold is associated with tetradymite, chalcopyrite and galena in cracks of pyrite crystals; these serve as indicators for Au-mineralised pyrite. The pyroelectricity coefficients of pyrite vary along the fault zone, with N-type dominant and small amounts of P-type pyrite at Fujia and Hedong. From south to north, pyrite with (100) crystal form decreases and pyrite with (111) or (100)+(111) form increases. Trace elements Bi, Te and high Se and Ni are positively related to Au. Average decrepitation temperature increases and frequency decreases from north to south; very high Au is found in pyrite with a decrepitation temperature of 150-200 rather than 230-270 degrees C., The NE-trending fault cuts biotite granite and K-feldspar porphyroblastic granodiorite. Along its 8 km are four medium-sized deposits, Jiehe, Shangzhuang, Hedong and Fujia, in altered rocks of the fault shatter zone. Ore microscopy has shown that native gold is associated with tetradymite, chalcopyrite and galena in cracks of pyrite crystals; these serve as indicators for Au-mineralised pyrite. The pyroelectricity coefficients of pyrite vary along the fault zone, with N-type dominant and small amounts of P-type pyrite at Fujia and Hedong. From south to north, pyrite with (100) crystal form decreases and pyrite with (111) or (100)+(111) form increases. Trace elements Bi, Te and high Se and Ni are positively related to Au. Average decrepitation temperature increases and frequency decreases from north to south; very high Au is found in pyrite with a decrepitation temperature of 150-200 rather than 230-270 degrees C.

Exploration drilling in the western part of the Klokoc skarn deposit intersected a quartz diorite porphyry hosting disseminated epithermal gold and pyrite with some chalcopyrite and galena, at 213 m depth. Minerals identified include hessite (Ag2Te), petzite (AuAg3Te2), telluro-bismuthite (Bi2Te3), tetradymite (Bi2Te2S) and Ag-Bi sulphotelluride with electrum., Exploration drilling in the western part of the Klokoc skarn deposit intersected a quartz diorite porphyry hosting disseminated epithermal gold and pyrite with some chalcopyrite and galena, at 213 m depth. Minerals identified include hessite (Ag2Te), petzite (AuAg3Te2), telluro-bismuthite (Bi2Te3), tetradymite (Bi2Te2S) and Ag-Bi sulphotelluride with electrum.