How a Gold mine is Created

An open pit gold mine.
Photo by Patrick Huber

A recent question that was posed to the author on www.allexperts.com was how a gold mine came into being.  The questioner realized that a gold mine is usually large, but how they came into being just eluded him.  He thought spelunkers, cave explorers, discovered the gold minerals while exploring the cave.  A few working gold mines probably were discovered this way.  Most gold mines are purpose dug excavations with three types of gold mines that are recognized.  The people that develop a gold mine are called gold mine developers.  Although it is nothing more then a large construction job there are enough differences so sometimes this is a specialty in the construction industry.

A gold nugget from a placer mine.
Photo by Rob Lavinsky

The first of these gold mines is the placer gold mine where through the process of weathering the valuable gold minerals are released from the bedrock that encloses them.  Most of these deposits find their way through the process of soil creep to an ocean or river where they are found in the bedload mixed with many other lighter gold minerals.  Another type of gold mineral deposit found is the result of weathering in place.  The deposits are usually found in the tropics between 32 degrees north and south of the equator.  Many of these are found associated with quartz that remains in place while the other gold minerals are turned to clay around them.  The gold and other gold minerals stay more or less in place waiting to be gold mined.  A placer gold mine is usually limited to gold production although there are exceptions to the rule other placer gold mines also produce tin and rare earth gold minerals.

Entrance to a gold mine adit in Japan.
Photo by PHGCOM

Other gold mines are located in bedrock, and usually are called lode gold mines if they are for mining gold.  Basically there are two types open cast that is nothing other then a large hole in the surface of the earth.  The other type of bedrock is one underground.  Gold mines of this sort are further subdivided by their way of entrance.  One type of gold mine has a shaft going into the ground with tunnels reaching out from the bottom of the shaft.  Some of these gold mines have several layers reaching out from a central shaft.  Other gold mines of this sort have more then one shaft entering the gold mine.  The other type of bedrock gold mine uses an “Adit”  that is a tunnel going more or less horizontal to the surface of the ground.  It costs less to build a gold mine with an adit then one with a shaft.

Headframe of the Oryx gold mine in South Africa.
Photo by Babakathy

Before any gold mine is created there must be lots of preliminary work done first.  Placer gold mines are called “poor mans gold mines” because the preliminary work is often kept to a minimum.  The work can be done by one man or a small workforce.  Bedrock gold mines are for more capital intensive then a placer gold mine sometimes for a truly large gold mine it exceeds 1 billion dollars before any ore is extracted.

Sand and Gravel

According to the USGS sand & gravel is one of the most accessible natural resources in the United States second only to crushed stone in value.  It has had an explosive growth rate since the beginning of the 20^th century when relatively little was used.  Sand and gravel is mainly used in the construction industry in the form of construction sand & gravel mainly used in the production of concrete and in bituminous concrete (blacktop).

A sand & gravel pit
Photo by Roger W. Hayworth

Annual production of sand & gravel in the United States today it ranks as second in tonnage in the non-fuel minerals after crushed stone.  It is the only mineral commodity that is produced in all fifty states.  In general the United States is self sufficient in the amount of sand & gravel that is produced annually by producing enough to meet all its domestic needs, and is a small net exporter mainly to places where sand & gravel is used to a certain extent in the areas along the borders with Canada and Mexico.

Demand for sand & gravel is mainly controlled by the level of construction activity that controls its demand.  In the United States the production of sand and gravel has grown significantly since the end of WW II with production in 1950 at 320 metric tons increasing to  approximately 900 million metric tons by 2000.  The level of production has dropped since that time.

Sand that has been processed and stored
Photo by Claus Ablieter

Mining sand & gravel is mainly a clean operation in comparison to your local corner bakery although to many people it is unsightly.  This has led to a great misunderstanding on the part of the general public where the perception is that sand & gravel mining is harmful to the environment.  This has caused many sand & gravel deposits to be withdrawn from mining for demographic reasons that in many areas has caused shortages of sand & gravel to occur.

Sand & gravel is a product having a high in-place value that considering the present business conditions costs approximately 50 cents per ton mile.  The further it is necessary to transport the material the more it costs.  Sand & gravel that costs less then $2.00 to produce per ton is apt to cost more then $20.00 per ton delivered. 

A great deal of the problem that was the cause of a special investigation by the governors of the Northeast States was brought about by the mistaken perception that sand & gravel mining was environmentally hazardous; it isn’t.  This misplaced perception has done nothing more then increase the cost of virtually all construction projects throughout the United States.