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Friday, June 29, 2012

Time and Stratabound Ore Deposits:

Native copper
Photo by Rob Lavinsky

Time and strata bound ore deposits are formed because of a specific geological event that causes the deposition of ore.  This ore is not necessarily deposited at the same time as the rocks, but can be the result of a later infusion of metal bearing liquids with a chemical reaction depositing the metals from solution.  A typical reaction may occur between the solution and organic components in the host rock.

Another type of time and Stratabound deposit is volcanogenic massive sulfides.  These deposits are the result of metal sulfides being the first minerals to form in a magma, and sinking to the bottom of the magma chamber due to their higher density over the other components of the magma.

A common form of this kind of ore deposit is one that forms where there is a fossilized log jam in the bed of a paleostream deposit where the logs provide a large bed of organic matter that can be replaced by later mineral bearing fluids. 

These fluids are generally the result of volcanism, and are coming from both groundwater sources and juvenile waters that are expelled from the magma as it cools.  These waters can also dissolve metals from the surrounding country rock as they are passing through then.  The majority of ore deposits are of this type.

Another type of Stratabound deposit occurs when you have a paleo-karst terrene where the mineral laden waters follow the overlaying sediments that are usually sandstone that has also filled the nooks and crannies in the karst terrene.  An example of this is the lead/silver deposits that were mined in Leadville, Colorado.

The presence of petroleum can also supply a source of organic materials to trap metal bearing solutions and make them give up their riches.  This usually happens in volcanic intrusions into sedimentary rocks that produce enough heat to turn some of the petroleum into an analog of amber called “Pyrobitumen.”  This often happens in back arc basins like the Sea of Japan.

The metals are usually deposited anywhere they meet with a reducing environment.  A back arc basin is one of these places.  A marine basin is another of these places, and a good modern example is the Mediterranean and Black Seas.  Other then the mane made Suez Canal this large area of seawater only has one natural entrance and exit the Straits of Gibraltar.  The waterflow is restricted through these straits due to their narrowness, and shallowness.  The waters from the Atlantic flow inwards along the bottom, and the water from these seas flows outwards from the top.

Most of the world’s ore deposits are found in Time and Stratabound deposits. 


Cisternas, M. Eugenia, et al. The role of bitumen in Stratabound copper deposits in the Copiapo region of Northern Chile, Springerlink,  

Prospecting in Gabbro

Gabbro a dark colored mafic rock
Photo by Tanno4595

Gabbro deposits are noted for their polymetallic sulfides that are often associated with the base of the intrusion in the form of Volcanogenic Massive Sulfides caused by settling of the sulfides to the bottom of the intrusion.  They are usually found on the footwall of the intrusion where it meets with a different kind of rock that was intruded. This is assuming that the intrusion was injected in one shot as many of them are.

If the intrusion underwent more then one injection of magma you are more likely to have a series of bedded ore bodies that are at the bottom of each individual injection as a result of segregation of the components of the magma.  These are primary ore deposits derived from the magma itself.

The ores most apt to be found associated with a Gabbro intrusion aside from iron pyrite and phyrottite are the sulfides of nickel and copper with accessory mineralization of chromium, silver, gold and platinum group metals (PGM).  More often then not these are segregated into the volcanogenic massive sulfides (VMS) at the bottom of the intrusion, or if the intrusion cooled quickly dispersed throughout the body of the intrusion. 

Some good examples of Gabbro intrusions exist on opposite ends of Connecticut.  The first intrusions of interest are located in Torrington and Litchfield they are the Hodges Complex in Torrington, and Prospect Hill in Litchfield.  Both of these prospects have had producing copper-nickel mines located on them during the early 1800s.  They were also explored for nickel after WW II.  Hodges Complex by Falconbridge mining from Canada and Prospect Hill by Dino Testone a local prospector who owned a diamond drilling rig.

In the case of the Hodges Complex not enough ore was found to make a modern mine.  The Prospect Hill Complex was another story, the diamond drill turned up a large quantity of nickel ore, but Mr. Testone passed on before he could develop a mine as told to the author by Mr. Testone.

At a later time with another geologist the author did a bedrock mapping project on the Hodges Complex and found it to be divided into three lobes that they were norite interbeded with an untramafic rock called pyroxenite.  We found several minerals in the intrusion including: ilmanite, sperrylite, erytherite, chalcopyrite, cordierite, pyroxene, labradorite, plagioclase, serpentine, and pyrite.

Both of these intrusions were diatremes that from other like diatremes were injected as wine glass shaped intrusions.  Most of the separated minerals were out of sight, and probably at the bottom of the intrusions, or in their footwalls.

The other two intrusions are located in Eastern Connecticut.  The first one is the Preston Gabbro located in the towns of Preston and Ledyard.  Most of these intrusions are found on the lands of the Mashentucket Pequot’s and on the grounds of their casino “Foxwoods.”   According to their former chief Richard Hayward in a telephone conversation several years he told the author that they found platinum in the drill cuttings when they were drilling wells for Foxwoods.  There is a platinum nugget on display in the Wesleyan University Science Museum that came from the river draining this intrusion.

There is another intrusion of Gabbro to the Northwest just below Willimantic that may be a larger part of the Preston Gabbro that could be connected below the younger rocks that form its roof.  It will take some drilling however to prove this however.

To prospect in either of these intrusions probably the best place to look for mineralization is in their footwalls where any sulfide minerals might have collected.  This may be done looking for magnetic anomalies or by core drilling.

The State of Connecticut maintains records of wells that have been drilled in the state at DEP Headquarters, 79 Elm St., Hartford, CT.  This is a good place to look because this is the office of the State Geologist as well as the Reading Room for State Environmental Records.  It also houses the DEP Store that sells State Publications.

Another nearby source of information is the State Library on Capitol Ave. across the street from the State Capitol.  They keep aerial photos reaching back to 1934 as well act as a government repository for documents published by the US Government.


General Types of Auriferous Deposits, Alluvial Exploration and Mining,

Bedrock Geological Map of Connecticut, Compiled by John Rodgers, 1985,

Friday, October 28, 2011

How a Mine is Created

An example of a shaft mine, the Oryx Mine in South Africa
Photo by Babakathy

A recent question that was posed to the author on was how a mine came into being.  The questioner realized that a mine is usually large, but how they came into being just eluded him.  He thought spelunkers, cave explorers, discovered the minerals while exploring the cave.  A few working mines probably were discovered this way.  Most mines are purpose dug excavations with three types of mines that are recognized.  The people that develop a mine are called 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.

An excavator and trommel in action at a placer mine in Alaska
Photo by Dennis Garret

The first of these mines is the placer mine where through the process of weathering the valuable 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 minerals.  Another type of 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 minerals are turned to clay around them.  The gold and other minerals stay more or less in place waiting to be mined.  A placer mine is usually limited to gold production although there are exceptions to the rule other placer mines also produce tin and rare earth minerals.

Loading ore at an open pit mine in Nevada.
Photo by Cornelius M. Keyes

Other mines are located in bedrock, and usually are called lode 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.  Mines of this sort are further subdivided by their way of entrance.  One type of mine has a shaft going into the ground with tunnels reaching out from the bottom of the shaft.  Some of these mines have several layers reaching out from a central shaft.  Other mines of this sort have more then one shaft entering the mine.  The other type of bedrock 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 mine with an adit then one with a shaft.

An adit leading into an underground mine in Australia.
Photo by Flagstaffotos 

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

Monday, October 24, 2011

Introduction to Mining

This piece of art is composed of earth materials.

There are about 7,000 active mines on the face of the earth as we speak for a wide variety of minerals and ores that are produced to support our way of life and indeed our civilization.  The products from these various minerals range from arsenic to zirconium with the minerals in demand at a particular moment in time causing a situation that might just as well be called, “The Mineral of the Month Club.”  Another way to put it is what mineral is in style?

It seems that at this moment the supply of rare earth minerals (REM) are scarce. The hunt is on worldwide for these minerals that at present are mainly found in the clay deposits of China.  The Chinese, the world's largest producer of REM have restricted the export of these elements from China causing a worldwide search for REM minerals or replacements for them. This has become finding these minerals a high priority for prospectors worldwide.

This Rolls Royce Phantom was also made from earth materials.
Photo by Brett Weinstien 

From these mines are produced many of the things that we take for granted. In two of the products produced from mines that account for some of the highest tonnages are sand and gravel, and crushed stone. For the most part these commodities are invisible to the average person although our civilization is built upon them. There is hardly a facet of our civilization that is not touched in one way or another by mining. It is man's use of these materials upon which our civilization is built. If there were not further products of various minds we would probably still be living in trees. The oldest mine in the world is located in Eastern Africa is the Lion Mine that produced iron ore that was used by early man for decorating his body about 70,000 years ago.

Mines are the source of all the metals you see in buildings, cars, airplanes and all household products you see around you. They also produced many of the raw materials that were used in construction. Other minerals are used in the chemical industry. The energy industry is also a large user of other minerals like coal or oil or uranium. Uranium itself accounts for a good share of electricity that is used in the world. Some of the largest deposits of uranium bearing minerals are found in northern Saskatchewan.

Although you probably do not see the connection between the paper industry and mining it exists because some of the minerals like limestone when it is crushed into a fine powder is used as a sizing in the manufacture of paper. A good share of this powdered limestone is produced in northwestern Connecticut by Minteq. More powdered limestone as calcium carbonate is mined by Minteq in North Adams, Massachusetts this USP certified for use in medicine. Just think the next time you take an antacid it was dug her from the ground in Massachusetts.

Gold is another metal produced from mines it is not only beautiful when used in the manufacture of jewelry it also has a high monetary value, and is used in many industrial applications such as electronics and even in the aerospace industry.

Mining is decrying being many because of their minds minors are displayed on the earth. The truth is mankind has gotten to be where it is because of its ability to make use of earth materials. Those who think otherwise are either ignorant or foolish, but this feeling is nothing new that occupies most of the first chapter in De re Metallica the first book on Mining engineering written in the early 1500s by Georgius are you Agricola. The first chapter of this book is devoted to exactly the same subject, and Agricola was writing about the same kind of people.

Saturday, October 22, 2011

Ontario’s Ring of Fire

Chromite the mineral of interest in Ontario's Ring of Fire
Photo by Andrew Silver   USGS

Located in northwestern Ontario the Ring of Fire promises to become a decades long mining project.  Although the project promises to become a benefit to the local community it is alarming the local residents and the environmentalists.  These extensive deposits have been discovered just outside Thunder Bay, Ontario causing the mining participants to circle the area, and positioning them to share in the future steel market.

The mineral of attention is chromite, a dark colored ore of chromium that is used for the manufacture of stainless steel and to a lesser extent for chrome plating.  To a lesser extent it is used for tanning leather making use of potassium or sodium chromate in the chrome tanning process.  The chromite deposits found in the Ring of Fire have been dubbed as the greatest deposits of chromite in North America by the Ohio based company Cliffs Natural Resources (NYSE: CLF) that is convinced the deposits of chromite are worth fighting for,  The potential deposit is located under water and rocks close by to major highways and railroads making shipping the ore simple and cost effective.

The region is located near Kenora in western Ontario in an area of muskeg known as the James Bay Lowlands centered on McFaulds lake 500 kilometers northwest of Thunder Bay. The first discovery was made by Noront Resources LTD, a mining company that was in the area in 2007.  On August 28th they announced they had made a large find on the basis of two holes that were drilled.  The first core revealed a strong showing of copper sulfides, and the second had similar results.  A bit later Noront announced they had copper, nickel, platinum and palladium.

Cliffs call this monstrous deposit of chromite the Black Thor Deposit that would place Canada as a player in the worldwide chrome market of which South Africa is the world’s largest producer.  They declare this is the largest deposit to be found in North America.  Chromite is used in the steel industry to produce ferrochrome a precursor of stainless steel where it is battling with China to maintain its dominance of the market.

There are many roadblocks facing Cliffs that is based in the US, not least of which is satisfying both federal and provincial environmental regulations, but it has the added burden of satisfying the members of the First Nations locals that live right in the middle of the deposit.

The representatives of the First Nations communities in the area have called for participation in the review for development of this deposit of chromite in their region.  The Canadian Environmental Assessment Agency has recently issued a statement that the locals are being overlooked in the permitting process.  It is this agency that will take the reigns to study that will determine the access, if any, that the chromite miners will have in the area.

Cliffs wants to construct a processing plant at the site of a former iron mine that will be known as Moose Mountain that was closed over forty years ago.  The proposed plant would process the ore from the McFaulds Lake mine that has been dubbed the “Ring of Fire.”  The proposed plant is located near Caproel, Ontario.

If the project is approved construction of the mine would commence in 2015 with a large enough deposit capable of being mined for at least thirty years.  The deposit produce an estimated million tons of chromite concentrate per year as well as several hundred thousands of ferrochrome per year as reported in the Sudbury, Ontario Star.

Opening the area to development could produce approximately 1000 new jobs if the project is allowed to go foreword with about 500 of them near Caproel.  The other 500 jobs would be at the McFaulds Lake mine.  Needless to say Ontario’s Ring of Fire has attracted a lot of junior explorers to the region having potential world class deposits of chromite.

Tuesday, January 18, 2011

How the Chinese Shot Themselves in the Foot with Rare Earth Metals

During the early part of the 1400s, Eighty-Seven years before Columbus discovered the New World the largest Bluewater fleet in the world belonged to China. During the period from 1403 to1433 this great fleet was under the command of the Chinese explorer Zheng He during that period He made seven voyages to explore the Western World. According to contemporary records he got as far as East Africa, and there are many rumors that he also discovered the Americas. There is even one rumor that one of his fleets rounded the southern tip of South America at Cape Horn.

Chinese Junks fighting in Viet Nam

Some of these ships were huge carrying as many as nine masts and weighing more than 1500 tons. The ships were also capable of carrying more than 1000 passengers. This all came to an end around 1433 when at the whim of the Chinese Emperor the entire fleet was put to the torch ending China's dominance of the seas to this day, and China turned its back on the rest of the world for centuries.

In the latter part of the 20th century China had a virtual stranglehold on the supply of rare earth metals (REMs) because of large deposits present in southern China in clay. The Chinese even perfected the extraction of REMs from this clay becoming the largest producers of REMs in the world. According to one of the prime ministers of China, China was going to be the Saudi Arabia of REMs.

This is a slab of laser glass containing REMs for use at the National Ignition Facility

Since REMs are so essential to the technology of the 21st century virtually the entire mining community of the world went on a search for new sources of these metals. This should have given the Chinese leadership some food for thought had they listened to their scientists instead of listening to their ideology. Instead of being rare in the Earth's crust REMs are fairly abundant some of these metals are actually more abundant than copper.

The scientists of the Western world used their knowledge for not only finding new sources of REMs, they have also developed new ways of making things like rare earth magnets that either use less REMs or have replaced them using other metals. These actions have reduced the demand for REMs from China. That begs the question, “Have the Chinese once again shot themselves in the foot?”

Friday, January 7, 2011

Mining Sand & 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 20th 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 mine

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.
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. 

This is a reclaimed sand & gravel mine note the conveyor belt in the background with piles od sand.

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.