Alluvial Gold

Romania is known as a gold-rich country, one of the richest in Europe, distinguished by an area called the Golden Cadrilater in the Apuseni Mountains, with two major golden types: gold in in situ mineralization, and alluvial gold from sedimentary deposits in riverbeds.

The alluvial gold present in the riverbeds and terraces resulted from the erosion of the rocks over time. The rivers flow over the gravel, washing, separating and concentrating alluvial gold and heavy metals into specific layers.

Our rivers bear gold

The territory of Romania has a very complex geological structure. Most of the territory is part of the Alpine orogenic area with tertiary and current volcanism. It consists of young mountains, hills, plateaus and plains intercalated in tectonic depressions, containing, as a whole, rich and varied deposits of useful mineral substances such as: mineral fuels, ores of precious metals, ferrous metals, non-ferrous and rare metals, non-metallic substances, etc. The presence of many useful mineral deposits in Romania has greatly influenced the country’s economic status. Metalliferous ore extraction and processing has experienced periods of growth or regression during time.

Among the exploited metalliferous deposits in Romania, a special place is held by the gold- silver deposits. Over time, several gold mining areas have been discovered and outlined on the territory of Romania, with a unique golden deposit in the world, consisting of at least eight large-scale ores estimated at 54 billion dollars.

The gold flows, literally

In Romania, with the exception of some lesser golden concentrations, which in large part have already been exploited, we distinguish the region of the Metaliferi Mountains where the well-known Rosia Montana is lcated. Gold deposits located in Transylvania between the Mures rivers in the south and Aries in the north are located in a sub-unit, well individualized structurally, petrographically and morphologically, known as the Metaliferi Mountains, within which it is delimited the so-called “Golden Polygon of the Apuseni Mountains”, which has its peaks in the settlements of Baia de Aries, Zlatna, Sacaramb, Toplita and Caraci.

Alluviums are thin deposits, in the form of layers, made of material transported by flowing waters, sediments on the bottom of the riverbed, on the meadow or at the water spill. They are made up of boulder, gravel, sand and mud. If they contain noble metals (gold and silver), they are called golden alluviums.

The outcrops of primary gold deposits usually located in mountainous areas are physically and chemically disaggregated with host rocks under the action of atmospheric agents. The detritus resulting from disaggregation is transported by water and further minced, with a sedimentation occurring in the order of the specific weight of the component minerals.

The precious noble metal

The deposition is influenced by the sinuousness of the river bed, the speed of water circulation, the irregularities of the thalweg, the obstacles encountered in the path, the geometric shape of the granules and the entrained fragments. On the thread of the water courses a natural mechanical preparation of the eroded material takes place, the heavy fragments being deposited, and the light ones being carried away along with the river stream.

Heavy minerals, along with gold, concentrate on points where the water course changes its direction in convex parts or swirls. When floods occur, the river meadow is covered with waters, and new alluviums are deposited over old ones. In these flattened alluviums, significant golden concentrations can occur at the base of the alluvium, favored by the greater weight of the metal granules.

Due to the dissolution of silver that accompanies gold, chemical concentration also takes place. For this reason, alluvial gold is poorer in silver content compared to strand gold. Under the action of infiltration waters, a separation of grains and golden sheets is produced, which from the surface, gradually descends to the base.

Ecological exploitation of alluvial gold

For the exploitation of the golden alluviums, simple old-fashioned traditional washing methods have been used since ancient times and even in modern times. Their use is based on the tendency of gravitational separation, under the influence of water, of gold in the sands flowing on an inclined plane, due to the specific gravity greater than that of the accompanying material. The technique of gold recovery from golden sands is known since ancient times, described by Plutarh, Strabon, Plinius and Diodor from Sicily. For this purpose, buddle (“saitroc”), woven sieves and burned clay boards were used. These boards were rounded, with a very good drainage opening, having on the inner bottom and on the side walls some quartz claws, fixed in clay before burning. These claws were designed to prevent gold grains from rolling freely on this board, fulfilling the role of wool skins used by Greeks in the gold washing process.

In the contemporary era, alluvial gold is extracted through high-tech equipment, based exclusively on mechanical, gravitational and centrifugal processing, which take the primary material from the river bed or terraces through high-performance slurry pumps or excavators then it is washed with high pressure water, sorted into vibrating screens, after which the coarse gold is captured on the Sluice Box gutters and the useful material is gravitationally separated and centrifugally concentrated in Knelson type concentrators. Following these procedures, the fine concentrate from Knelsons is directed to Gemini-type separating tables to process and set the final product, which is then melted in the furnace and poured into ingots.