EPR-CHARACTERISTICS OF QUARTZ FROM GOLD DEPOSIT MURUNTAU (UZBEKISTAN)
Keywords:
quartz, quartz vein, electron paramagnetic resonance, Е1’-centre, paramagnetic Al–O–-centre, Muruntau, Uzbekistan.Abstract
We studied quartz from gold deposit Muruntau in Uzbekistan by the method of electron para-magnetic resonance (EPR). The deposit began to exploit in 1976 by a pit and is still ongoing. The deposit is located in phyllite-like shales and sandstones of the Upper Proterozoic. Mineralization has been traced to the depth of 4–5 km. Most industrial mineralization is in a zone of phlogopite-orthoclase-quartz metasomatites. The main productive association is gold-scheelite-quartz. Geochemical fields of gold (<< 0.1 g/t) and tungsten (> 0.003 %) are combined in the circuit of metasomatites, as well as the abnormal field of U, Th and K. The highest content of gold (> 10 g/t) is confined to the rachidal quartz veins, which have a lenticular structure, the length up to 250 m (medium – 100–120 m), the ca-pacity is a few meters. We studied two varieties of quartz: 1) milky white fractured quartz with visible inclusions of gold (19 samples) and 2) white quartz with inclusions of host rocks, pyrite and arsenopyrite, without gold (12 samples). First, the EPR-spectra were recorded at room temperature (300 K). Paramagnetic E1’-centre has been fixed in the quartz samples; it belongs to its own radiation defects and is formed under the influence of natural radiation during the growth of quartz. The results showed that in the gold-bearing quartz the number of E1’-centres is from 0.33 to 0.40 conventional unit, while in ore-free quartz it is from 0.10 to 0.24 conventional unit, i.e., the quartz of the second group is less defec-tive. Further, we recorded the EPR-signals at the temperature of liquid nitrogen (77 K). We studied the presence of Al–O–-paramagnetic centre in quartz. It is known that the presence and amount of Al–O–-centre in mineral is an indicator of temperature, growth rate, pressure and composition of the environment. It turned out that the intensity of the EPR-signals of the centre in the samples of the first group is in the range of 0.60–0.86 conventional unit, and the second – 0.1–2.4 conven-tional unit. In addition, the appearance of the EPR-spectrum in the first group samples corre-sponds to the usual EPR-signal with good crystal structure. We can assume that during the forma-tion of Al–O–-centre quartz captured impurities and inclusions, in particular, he could capture as gold ions Au+, and native gold. Thus, the amount (intensity) of paramagnetic centres in quartz is a genetic affiliation of the studied quartz, its geological history. We proved on the example of the Muruntau-deposit using EPR the ability to distinguish ore and non-ore quartz.
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