САМОРОДКИ ЗОЛОТА - МОРФОЛОГИЧЕСКИЕ ОСОБЕННОСТИ

Abstract

There are three points of view about origin of gold nuggets: 1) endogen formation; 2) growth in gold placers; 3) formation within weathering crusts, due to dissolution of small sized gold particles. The first concept is the more supported one now, but the question «why gold nuggets are found mostly in gold placers» (more than 90 %, after N. V. Petrovskaya) remains unanswered. For this purpose, the primary documentation was studied for about a thousand gold nuggets weighing more than 50 g from numerous mines of Yakutia and Magadan region. In addition, there were systematized the published data on other gold-bearing regions of Russia and some foreign countries. Charts showing dependence of dimensions of gold pieces on their weight arc plotted. Length and width of nuggets are directly proportional in average to their weight. Thickness of nuggets weighing lesser than 4 kg increases, in average, linearly also, but for the bigger nuggets any valuable dependence of their thickness on weight is absent (makes in average 7-8 cm with 3-10 cm variations). This factor offers a conclusion that the large nugget thickness is limited by thickness of the host ore body, where the large gold aggregations were formed, i. e. that thin veins (basically lesser then 10 cm) are the most suitable occurrences for the nuggets formation. Within the veins nuggets are located in places with active precipitants of gold. These can be points of intersection with early formed quartz-sulfide veins or sulfidized partings in host rocks, or nesting concentrations of sulfides in the vein. While mining, those veins arc not developed in most cases because of their minor thickness and the low average grade of gold. From our point of view, this explains the sharp disproportion between amount of nuggets found out in placers and in primary gold ore deposits. Nuggets are rarely found in deposits with the minable ore-bearing thickness (1 m and more).