The Source of Gold – Its Ores and Minerals


With the high market prices of gold and silver in recent months, a number of people are wondering about where these metals come from. Gold and silver metals are obtained from a variety of different types of rock ores. Most people think of gold nuggets and such as the source of gold, but the truth is that very little of the new gold produced comes from nuggets – nearly all newly mined gold comes from ores mined from the natural hard rocks that contain gold in tiny, even microscopic particles. This article is created to describe what these ores are like. Gold is found widely diffused in nature even though it is one of the scarcer metals in the earth’s crust. Very commonly, gold occurs as the native metal encased within a mineral known as quartz. Sometimes the gold is in a finely divided state, sometimes in particles of considerable size, as nuggets, grains, scales, plates, threads and wires in quartz rock. It occurs also in a finely divided state disseminated through schistose rocks, slates and some sedimentary rocks like limestone. In these cases the rock has been altered by the flow of heated and mineralized waters, often resulting in the impregnation of large amounts of rock with silica, iron and a certain amount of gold. Sometimes the silicified rock even replaces much if not all of the original country rock. While historically speaking vein deposits were the most productive, these disseminated deposits currently yield much of the worlds gold ore.

Within gold ores, the element itself occurs in nature chiefly in the form of native gold, which is by far the most common gold bearing mineral. In various gold ores, the native gold commonly occurs as tiny particles contained within sulfide minerals such as pyrite. Iron pyrite is an exceedingly common mineral associated with gold, but it also serves as a reducing agent. Therefore whenever gold is found encased in pyrite, it is always present as free gold and not as some type of gold sulphide. Gold is also found at times in chalcopyrite, galena and arsenopyrite and stibnite, but not as a rule in such large amounts as may be found in pyrite. Other minerals, like sphalerite, pyrrhotite, magnetite and hematite sometimes carry small amounts of gold as well. Gold also occurs as tellurides such as calaverite. Common gangue minerals in gold ores include quartz, fluorite, calcite and pyrite, but many others can be found in smaller amounts.

Gold Ore Minerals:

The most prominent is native gold – most of the native gold contains a small amount of silver, copper, platinum, etc. Telluride minerals are the most common minerals which contain significant gold in their make up. They include: Petzite (Ag,Au) 2,Te, with a gold content of about 25 per cent. Hessite (Ag2Te), with gold often present replacing a part of the silver. Sylvanite (Au,Ag)Te2 : typically about 25 per cent. gold. Calaverite (Au,Ag)Te2 : typically about 40 per cent, gold. Krennerite (Ag2Te,Au2Te3) : gold is about 35 percent. Nagyagite (Au2,Pbi4,Sb3,Te7,S7). Some samples of Nagyagite have given upon analysis 12.75 per cent gold. The gold containing sulphides, as well as the tellurides, are of primary formation, although auriferous chalcopyrite might also be formed by secondary enrichment processes. Native gold may occur in the primary, secondary enrichment, or oxidized zones. The tellurides, which are usually associated with pyrite, are widely distributed, though not so abundant, but not always recognized; indeed by some miners they are mistaken for sulphides.

General Types of Gold Ores:

Gold deposits are often classified according to their association. The first of these may be catalogued as quartzose. This implies that the gangue mineral is acid, that is, quartz, and that fluorite may abound, or even the other gangue minerals of the alkaline earth group. Not infrequently there appears within the quartz varying amounts of pyrite and even limited quantities of chalcopyrite and galena. These are free milling ores. By a free milling ore, it is meant one that the rock does not require roasting before the gold can be recovered from it. Dry ore is the term often used for this category. The second class of gold ores is auriferous copper ores. These are widely distributed throughout the United States and much of the chalcopyrite is gold bearing. These auriferous copper ores are especially abundant in Colorado, Utah, Montana and British Columbia. They are also present at Gold Hill, North Carolina and in Canada at Newfoundland. The third class of gold ore is auriferous lead ores. The percentage of lead in these rocks is large and the gold content is often small. They are refractory ores like the copper ores. By refractory ore is meant one that requires roasting before extraction processing. The heavy sulphides as copper, lead and antimony require this method of treatment, that is the condition of the gold in the mineral will not allow of its immediate capture with most recovery systems. The fourth class of gold ores comprises the gold-telluride group. The gold telluride ores occur with silver, or with silver, lead and antimony, or as native gold accompanied by other tellurides. These ores are often sent direct to the smelters for treatment. A fifth type is the disseminated ore type. They are often low in grade but large. They fill large fracture and fault zones or replace certain geologic horizons. They are the result of the circulation of large amounts of heated water deep underground.

Some folks are interested in learning to recognize gold ores and seeing if they might have accidentally found some. To see photos of various types of gold ores and learn more about how to prospect for them, and where they come from, take a look at this web page: Gold Ore Photos and Information

For more information about prospecting for gold, see my: Gold Prospecting Encyclopedia

Chris Ralph writes on small scale mining and prospecting for the ICMJ Mining Journal. He has a degree in Mining Engineering from the Mackay School of Mines in Reno, and has worked for precious metal mining companies conducting both surface and underground operations. After working in the mining industry, he has continued his interest in mining as an individual prospector.


Sapphire Mining In Rock Creek Montana


When people think of sapphires they don’t often ponder where they came from or how they arrived in their local jewelry store. However, sapphires have an interesting history that parallels the old gold rush in the late 19th century.

Sapphires have been mined in Montana since the 1800’s and were viewed mainly as a by product of mining for gold. In fact, the production of sapphires didn’t flourish until 1892 when prospectors came across the Gem Mountain Sapphire deposit of Rock Creek, Montana.

Visitors from all over the country visit Gem Mountain Sapphire deposit for gravel washing and sapphire hunting. People can purchase a 5 gallon bucket already filled with gravel to search through. Visitors are instructed to wash the gravel by hand with 12″ screen boxes. It doesn’t take long to realize that washing the gravel does take finesse in order to do it quickly and accurately. When the gravel is finally washed the box is then turned onto a table and the search begins. If visitors have washed the gravel correctly, all sapphires should be concentrated towards the center, making them easy to find.

After a few pieces of rough material is collected, they are then taken in for further examination. Everyone usually comes away with a few small stones that would be worthy of collection. Visitors then have the option of heat treating the rough sapphire crystal to bring out a deeper more attractive color. They are also assessed for cut and faceting potential. Gem Mountain even offers the option to set your polished gem in a jewelry setting for safe keeping and memories.

Gem Mountain actively mines for sapphires from May to September and produces about 22,000 to 25,000 cut stones per year for customers. During the off season, the mine stockpiles gravel to sift through at a later date in order to provide sapphires and gems to the local town of Philipsburg, Montana.

Overall, the Gem Mountain property in Rock Creek Montana offers a unique family outing and fun educational experience in the world of natural sapphire mining. People love the idea of looking through piles of gravel only to discover their very own sapphire-in-the-rough. The experience is fun for all members of the family and helps to keep the local area and businesses prosperous. The largest piece of rough sapphire crystal found at the mine was 39.41 carats! Perhaps this is part of the allure of the property, a hope and desire to find your own very large sapphire crystal.

Carl is a diamond and gemstone enthusiast with a particular fondness for sapphires. He often writes about popular diamonds brands like Hearts on Fire and Forevermark diamonds.

All You Ever Wanted To Know About Diamonds – But Never Thought To Ask

ImageEvery woman knows that diamonds are their best friend. Plenty of money has gone into successful marketing campaigns to drill down the fact that diamonds are rare and precious. Is this true or is it just marketing hype?

First of all diamonds are pure crystallized carbon that was formed deep within the earth’s crust anywhere from 1-3 billion years ago. Yes, it has been estimated through scientific methods that diamonds are indeed that old. On top of that diamonds are extremely durable. After all, if they are still here 3 billion years later.

Diamonds score a ’10’ on the Mohs hardness scale. This means that diamonds are the hardest natural substance found on earth. That is why they are recommended for jewelry items. They simply don’t scratch, crack, scuff, or break like other softer gems.
Diamonds are also used for industrial purposes. Various industries utilize the inherent qualities in a diamond to help cut and grind other materials. For example, diamond tips are regularly used for drill bits and diamond powder is a well-known abrasive material. This helps in cutting materials widely used like glass, steel, acrylic, etc. These industrial diamonds are quite commonly found and thus are not rare or precious. However, their inherent properties make them very useful for these industries and will continue to be used heavily.

Gem quality diamonds on the other hand are another story. Diamonds that are less than 1ct are far more common than a single stone that is great than 2 carats. That is why larger diamonds of high quality are actually extremely rare. These diamonds are typically sent to independent laboratories located around the world to help sort and categorize them for the commercial market. These labs do not set a value or pricing to them, however they do give an indication of how much a single gem can go for. For example, colorless diamonds that fall within the industry recognized D-F color grades are extremely rare. Therefore, these diamonds command a higher price premium than say a comparative “K” color diamond.

Clarity is also a very important characteristic that many diamonds are valued by. Clarity includes both internal inclusions and external blemishes. Since diamonds are a natural mineral, it is very common to have inclusions as part of the natural formation process. Therefore diamonds that are flawless are extremely rare and highly coveted.

Carat weight is the most important determinant to it’s price. It is for this reason that many diamond cutters try to maximize diamond carat weight, as they know they can get more for it on the commercial market.

Finally cut is the only characteristic that is man manipulated. Ironically, a diamond’s cut is the most important aspect to it’s ultimate brilliance and overall beauty. Remember, diamonds are found in nature as a rough crystal. It requires cutting and polishing to bring out a diamond’s natural brilliance. A well cut diamond is also very rare since most cutters would rather cut a larger “good” diamond and get more money for it as opposed to a smaller “ideal” cut diamond.

For many years the De Beers Company has had a monopoly on the world’s largest diamond mines and thus mined diamonds and kept them held in storage to control the supply and demand. However, De Beers has been forced to sell off some of their holdings because of consumer complaints and now many more players are entering into the diamond commercial market. There is now much more diversity to prices and many people can enjoy price comparisons to ensure that they are getting the best value for money. Today it is recommended to purchase diamonds online due to the larger inventory, cheaper prices and convenience. However as times continue to change, so will the diamond industry.