Milk fermentation helps explain the abnormal occurrence of gold veins

Milk fermentation helps explain the abnormal occurrence of gold veins
Milk fermentation helps explain the abnormal occurrence of gold veins
Anonim

Despite its low concentration in the earth's crust, gold often forms rich deposits - veins. The processes by which this happens have long remained a mystery to geologists. However, the clue came from where they expected least of all: fermented milk products resulting from flocculation (during fermentation) of the colloidal system (milk) served as a sample.

Milk fermentation helps explain the abnormal occurrence of gold veins

The hypothesis of flocculation of a colloidal system from gold nanoparticles into minerals rich in precious metal was tested in practice by Canadian scientists. They found rock samples from the Brucejack mine that matched the model perfectly. An article describing the study was published by specialists from McGill University and Pretium Resources in the journal Proceedings of the National Academy of Sciences (PNAS).

From the point of view of physics and chemistry, milk is a suspension of microscopic droplets of fat in an aqueous solution, that is, an emulsified colloid. Under normal conditions, the acidity (pH level, pH value) of this biological product is close to neutral. The structure of the milk is preserved due to the fact that the negatively charged balls of fat are constantly repelled from each other. This moderately stable interaction allows the colloidal system to retain its taste, appearance and smell, while not exfoliating.

However, if bacteria, which metabolize lactose into lactic acid, are added to milk, the pH level will begin to drop sharply. The colloidal system will lose stability: the surface charge from the microdroplets of fat will drain off, and they themselves will stick together. This is how milk is fermented and converted, depending on the preparation and type of bacteria, into yogurt, cottage cheese, fermented baked milk or other useful products. This process is called coagulation, or rather flocculation, its subspecies with the formation of loose intermediate structures.

Milk fermentation helps explain the abnormal occurrence of gold veins

Quite a long time ago, geologists, physicists and chemists suggested that gold deposits could form in a similar way. Ground waters wash out the microparticles of gold contained therein from the earth's crust. As more and more associated substances dissolve in the liquid, its acidity increases. When it reaches a certain limit, the compounds of the noble metal cease to behave according to the "rules" of colloids - a charge flows from the surface of their microparticles, and they stick together.

The only problem was that such a mechanism had never been observed in practice. According to calculations, water with a gold content of only a few parts per million should have time to form veins weighing in kilograms in a matter of days. Thus, raising the concentration of the precious metal in the rock from the average for the earth's crust of four milligrams per ton (conservative estimate) to 41.6 grams per ton (ten and a half thousand times). Alternative hypotheses suggested a variant of gold sedimentation from solutions of chlorides or bisulfides, but this version has its drawbacks.

The achievement of Canadian scientists is the discovery of the long-awaited "intermediate" stages of vein formation. They found fragments of calcite, dotted with microscopic channels, in which electrum (a mineral that is a natural alloy of gold and silver) has settled.The nature of the "blood clots" in these "veins" with a diameter of about 50 nanometers almost unambiguously indicated that they had stuck together from smaller particles in the process of flocculation.

Well, full-size gold-bearing veins, respectively, are formed when a stream of precious metal-rich water passes through such a rock. It fills in microcracks and dissolves the surrounding minerals. When acidity increases, the colloidal system collapses and gold particles quickly clog all the wreaths. After a short period of time, small canals nearby almost merge and become a rich nugget or dwelling. A similar mechanism can occur in relatively large channels in rocks.

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