 2. Gamma-Activation Analysis of Gold-Bearing Ores. |
In the process of exploration and exploitation of gold deposits, ore sampling is a specifically difficult problem because gold in nature is distributed extremely irregularly and its quantities are very small. Hence, an analytical method is required to be capable to determine gold in sufficiently large analytical weighed samples with threshold of sensitivity not less than n*10-5% and high productivity. Traditional assay method requires complicated sample preparation, it is very laborious method and not rapid.
In connection with the above in 1973 rapid highly productive method for gold analysis which allows analysing of analytical weighed sample of ≈0.5kg with threshold of gold determination not less than 5*10-5% with productivity 300 thousand analyses per year to provide analytical works at Muruntau Deposit. Principles and equipment were developed and introduced in production process by the efforts of specialists from Navoi Mining & Metallurgy Combinate, All-Russian Scientific Research Institute of Exploratory Equipment and Scientific Research Institute of Electronic Physical Equipment. During a short term the Laboratory of Gamma-Activation Analysis was founded at Muruntau open pit and in April, 1977 the first commercial analysis was performed to determine gold concentration in the ore sample from Muruntau Deposit. The Laboratory is a unique one and it has no analogues in the world analytical practice. In the period of operation the Laboratory has performed more than 10 million analyses of geological samples. After the Laboratory commissioning it became possible to provide Muruntau mine (and since 1993 - Kokpatas gold-sulphide deposit) with on-line analyses.
Gamma-activation analysis method is based on sample activation by highly energetic gamma- quanta produced as a result of target braking of electron bunch from Linear Electron Accelerator (of high amperage current) (ЛУЭ - 8) followed by measuring of induced gamma-activity in previously weighed analytical sample. As a result of
197Au(γγ) 197mAu
reaction gold isomer with 279keV energy of gamma-
quantum is produced. The analysis process is completely
automated, analysis results are displayed and saved
in a computer external memory (data carrier), analysis
cycle is 17 seconds. |
Analytical weighed sample (450-550g) is packed into a 290cm3 pan. Method allows material analysis of any lump size which could be placed into a pan, so sample is ground only to provide representative sample. The experience shows that for quartz ores with medium lump size gold -1mm grinding is quite enough; but for sulphide ores with fine-dispersed gold 2-3mm grinding could be acceptable. Thus in the analyses carried out at Kokpatas, Daugyztau and Amantaitau gold - sulphide deposits we used weighed samples obtained by natural reduction of drilling sludge without its additional grinding.
· Features of gamma-activation method, namely - high penetrability of primary and secondary radiation allow developing of the principles of rapid analysis of gold for ore particles of 25-100mm lump size, which in its turn promoted accelerated development of radiometric methods of gold ore particles sorting at Kokpatas, Daugyztau and Muruntau deposits.
· Method of gold determination in dry jewelry scrap was developed. Such scrap analysis using traditional methods is very difficult in realisation.
· Method of phosphor determination according to correlation dependence with uranium, which currently is being used successfully in phosphorite mining.
· Standard samples (standards) are widely used in analytical control analysis. Our Laboratory successfully took part in evaluation analyses of the State Standards, which could be committed only to the first-class laboratory. As a result of such work we have a 50 standards collection.
· At present time the Laboratory provides our region with gold analyses annually performing more than 600 thousand analyses. In case of need, the quantity of analyses can be increased and frame of issues decided can be expanded. Works for method and equipment improvement are constantly being carried out. Works for spectrometry tracts modernisation, computer aided control for measuring system and linear accelerator are being performed. |
