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| 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 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.
References:
Maiden, KJ, et al, Regional controls on the location of
Stratabound copper deposits, Science direct, abstract, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBP-48B5BVS-9&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1129894181&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f1dc9cf34b161c53f88e513d56418aca
Cisternas, M. Eugenia, et al. The role of bitumen in
Stratabound copper deposits in the Copiapo region of Northern Chile ,
Springerlink, http://www.springerlink.com/content/c445014g82520508/
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