What Are the Different Gold Ore Types?

Gold is a comparatively scarce metal in the earth’s crust, but the huge market for the metal sparks the need for its extraction. Study of different types of gold ores then becomes important as a great deal of factors like metallurgical conditions, economic viability and resourcefulness of the gold depends largely on the type of ore that it is extracted from. Gold ores can be categorized under four broad heads: free milling ores, refractory ores, preg-robbing ores and complex ores.

Free Milling Ores

• Free milling ores comprise the most profitable gold ores. Quite logically, the ore types that fall under this category promise great gold recoveries, sometimes even up to 99 percent. The best positive with this ore type is that it can be easily crushed, washed and milled to recover the gold contained within it. However, these are rare in nature. The best example for this ore type is sugar quartz shot through with metallic gold. Quartzrose ores in general fall under this category.

Refractory Ores

• The ores that constitute refractory ores could entail lesser gold recoveries, which could at times even be as low as 50 percent. But nonetheless, this segment is equally important for the simple reason that free milling (more profitable) ores are too scare in nature to cater to the ever-increasing demand for the metal. The cost of extraction for these is high too, due to the expensive processes like roasting, bacterial oxidization and pressure oxidization required to get to the pure metal. Methods like cyanidation or leaching are also fairly popular to yield better gold recoveries and thereby increase the overall profitability. The refractory gold ores mainly comprise of submicroscopic gold deposits. Gold sulfides also contribute to major refractory ore deposits. Auriferous copper ores and auriferous lead ores are the major refractory ore types.

Preg-Robbing Ores

• At times, gold exists as cyanide solution-leached form in nature. The gold particles basically get lost by absorption into fine-grained carbonaceous material present in the ore. These ores are referred to as preg-robbing ores and these gold deposits are therefore extracted with much difficulty.

Complex Ores

• Complex ore is extremely tough (or even at times, impossible) to segregate from its natural source. Its extraction sometimes turns out to be largely unfeasible and often not taken up in the first place. Copper-rich gold ores are characteristic of this group.