All About Skarn

by Mark Osterberg, Ph.D | Jan 26, 2015 |

Take a Minute to Learn What Skarn Is and Why It’s Important

When precious metals mining companies explore for metals we can extract economically, we look for certain kinds of markers that signal a likely deposit. Different metals are associated with different kinds of markers.

 

What Is Skarn?

Skarn, an old Swedish mining term, refers to calcium-rich rock formations that have been subject to certain geologic processes. Skarn is a marker. Quite simply, finding skarn means desirable minerals and metals are likely to be nearby.

 

How Do We Find Skarn?

One way is through geo-magnetic surveys. The Earth has a magnetic field. Buried layers of minerals affect the strength of the field as measured at the surface. We’ve commissioned studies of magnetic data in the Star Mining District and it suggested there were significant “contact zones” (more on that in a minute) that were good candidates for skarn.

 

Having that data, we began a drilling program in 2012 and 2013 to extract core samples. The majority of the samples indicated significant skarn deposits.

 

Why Is Skarn Important?

It’s all about how skarn forms. Molten rock (magma) deep inside the Earth moves and circulates constantly. Over millions of years it pushes its way into crevices and openings in the crust. When it breaks through to the surface it produces volcanic activity. But most of the magma remains beneath the surface.

 

Eventually, as it moves toward the surface, it presses against sedimentary rock—primarily limestone and dolomite. Magma is extremely hot and dense. It contains water and a “chemical soup” of minerals. When it reaches a sedimentary rock barrier, it begins to cool. The cooling process gives off super-heated water mixed with other elements. As cooling continues over thousands of years, chemical reactions between the magma and the barrier rock create a “contact zone.” That zone becomes filled with rock that often holds mineable accumulations of metallic ores of iron, copper, zinc, tungsten, silver and gold. That calcium-rich rock is skarn. It’s a marker we look for.

 

What Happens in the “Contact Zone?”

Geological processes are complex, but here’s a quick summary of how that contact zone develops and why skarn is such a valuable find. Imagine millions of tonnes of magma pressing up against that sedimentary rock.

 

• Geologists use the term “intrusion” to describe what happens when magma forces its way into cracks and crevices. A key feature of this intrusion is the release of super-heated water that’s rich in silica, iron, aluminum and magnesium.

• These fluids mix in the contact zone and dissolve the sedimentary rock barrier, converting it to skarn in a process known as metasomatism.

• The term comes from Greek. Meta=change. Soma=body. Metasomatism is the process that changes the chemical composition of rock by introducing and/or extracting chemicals dissolved in fluids that migrate through the rock’s pores. Metasomatism often results in the formation of new minerals, especially metal ore deposits.

 

In everyday language, the extreme pressure and heat “wash” the sedimentary rock clean of its original minerals and replace them with more desirable metals. Skarn is that “re-mineralized” rock.

 

What’s Next?

We’ve analyzed core samples and large outcrops of bedrock that have come to the surface to give us a visual map of what we can expect to find when we dig. We also have data related to some historical mines that show the presence of skarn mineralization. Using this science we can estimate the presence of large skarn deposits beneath the surface of our property. Our next step involves further onsite testing, which you can watch by subscribing to our YouTube channel, or by subscribing to our newsletter to stay up to date on our latest activity.

 

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Mark Osterberg Ph.D

President/ COO

Dr. Mark Osterberg has worked for major gold and base metal mining companies and has over thirty years experience in the mining business. He has provided high level technical expertise to projects in the USA and overseas and has managed multiyear exploration and development projects as well. He has expertise and experience in porphyry copper and molybdenum systems, carlin-type gold systems, shear-zone and volcanic-hosted mesothermal gold systems, magmatic Cu-Ni-PGE and construction materials. His project related experience includes grass-roots, green-fields reconnaissance programs, brownfields exploration and development programs, mine geology and modeling. He has developed innovative mapping techniques for regional and mine scale programs, has excellent computer skills and is an expert GIS for Geology practitioner

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