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Technology of Recuperation Gold Fines & Ultrafines

Brazilian Experience
Starting from the distribution of gold in the different granulometric fractions of the feeding of the plant, it is verified that:

- the average tenor calculated of gold in the feeding of the plant is nearly 3.3 g/t (considering a density in situ of the mineral of 1.6 t/m3);

- the mineral presents 69.1% in fine masses under 200 nets (74 micras), which present 46.3% of the gold contained in the mineral;

- of the fraction of 200 nets, barely 7.4% in mass and 9.3% of gold in total are understood among this net (74 micras) and 10 micras, which shows the existence of 61.70% of fines under 10 micras which carry 37% of the gold contained in the mineral.

- the gross fractions present elevated tenors of gold distributed in an irregular form along the granulometry, with higher values in the fractions + 6#, = 28 + 35# and -65 + 200#.

In the results of the separation in dense-liquid, one verifies that there exist elevated percentages in weight of heavy minerals in gross fractions, which fall a lot in the finer fractions. parallel to it one can observe in these heavy gold tenors, of the order of tens of grams per tonneage in the gross fractions, which pass to the order of hundreds of grams in the gross fractions, which pass to the order of hundreds of grams in finer fractions than 28 nets.

Mineralogically the mineral is basically composed by quartz, and clay-limenites of varied porosity are added, iron oxyde with varied grades of hydration and clay-minerals. As lower constituents, the presence of iron sulphate was observed.

The floated product in dense media is composed essentially by quartz and clay addings, while being deepened it is constituted by addings of clay-limenites and iron oxydes.

We observed the presence of free gold barely in the finer granulometry than 28 nets (liberation net). In the gross fractions this occurs associated in the addings of clay-limenites and, starting from 28 nets, shows a liberation of the order of 95%, being the 5% remaining associated to addings which compose of the depth.

In the liberated fractions the gold is presented under the form of pellets with dentritic and equidimentional forms, being extremely strange the presence of laminated particles in the finer pelletmetries. Some grains are shown superficially impregnated by a particle of clay-limenite which comes to cover up to 30% of the surface of the same in the fraction -28 + 350, diminishing in the meantime in the finer fractions and being practically non-existant in the fractions below 65 nets.

With the objective of investigating the form of the gold occurrences, practices of separation were performed in scales of pieces of masonry including separations in dense liquids and electromagnetic separations. It was verified that the lights are constituted, essentially, by microcrystalline addings, quartz-clays with some limeniting, the gold associated is in mixed grains where it represents less than 4% of weight.

The intermediatries represent the same addings but with higher amounts of iron oxide associated. The gold represents less than 8% in weight in mixed grains. The gold contained in the liberated products are shown practically all free, those products are constituted basically by liberated cyrconite in the shape of nuggets.

In the thicker fraction, almost 50% of the gold contained is shown liberated in finer nets, that value reaches a maximum of 85%. The data obtained in the characterization of the rejection of the deslamators show that, at least, 25% of the 37% of the gold contained in the dislamated material is liberated.

The main general conclusions of these studies of characterization of the feeding and rejections of the plant of Salamangone, were the following:

a. the present gold in the rejections is, mainly, fine and ultrafine, non-recuperable by gravimetric processes;

b. almost 65% of the gold contained in the rejection of the dislamators are ultrafine, under 2 micras. What is retained in the gross fractions is found, in part, associated to addings pf quartz and/or clay minerals and/or iron oxydes, but mainly free, in an appropriate partition of 10% and 25% of the total content.