Mineral Exploration Geology

1
Mineral Exploration Geology

• Prospecting and the Exploration Process
• Reference Marjoribanks 1997. Geological Methods
  in Mineral Exploration and Mining. Chapman and
  Hall. Ch1.

2
Definition of Terms

• Exploration field activities take place as part
  of a strategy, often called a play.
• Large exploration plays are broken down into
  individual projects, often a particular tenement
  group, and each project may contain a number of
  prospects
• A prospect is considered to have the possibility
  of directly hosting an ore body and is usually a
  named geographic location. It could be
  outcropping mineralisation marked by old workings
  or it could be some anomalous geophysical or
  geochemical feature that has close spatial
  relationship with ore.
• An exploration geologists job is to generate new
  prospects and then to explore them in order to
  locate and define any orebodies which might lie
  within them

3
Generating New Projects and Prospects

• Prospecting generating new projects, from
  traditional panning of creeks to modern,
  sophisticated geophysical and geochemical
  techniques. Successful prospecting requires
  activity, observation, knowledge, insight,
  opportunism, lateral thinking and some luck.
• Today, it is unlikely that a prospector will
  stumble across an outcropping world class deposit
  unless exploring in remote parts of the world eg
  PNG, Central Asia. Thus exploration is
  increasingly focussed on the search for orebodies
  that have subtle outcrop or are buried beneath
  sedimentary cover eg Cannington.
• Prospecting success comes from several factors
• Searching where no one had searched before
• Identifying and testing subtle or non-typical
  indications of mineralisation that had previously
  been overlooked, either because they were very
  small or because some feature had previously been
  dismissed as unimportant.
• Lateral thinking testing new models,
  questioning all assumptions and accepted wisdom,
  being alert to small anomalies or aberrations.

4
Some Ways of Generating New Exploration Ideas

• New ideas may come out of the blue but more often
  are a result of detailed investigations into a
  specific research area.
• It often takes a bit of lateral thinking by the
  exploration geologist to take what is known in
  theory and apply this to the search for mineral
  deposits. Therefore it is important for
  exploration geos to stay in touch with the
  latest geological findings/theories.
• Eg New knowledge of geology or geophysics becomes
  available through a government initiative (eg
  AGSO). This information combined with your
  experience/knowledge of a certain mineralisation
  style may indicate the potential of
  mineralisation
• Eg A new theory/model becomes available such as
  plate tectonics and the realisation that
  continents are not static
• Eg A new technology becomes available
  magnetics, gravity, geochemistry
• Political changes make a certain area available
  for exploration eg China

5
Check-list of Negative Assumptions

• Before a project is abandoned it is worthwhile to
  critically check through a list of all the
  beliefs which are held about an area. They may
  turn out to be incorrect assumptions and you may
  be giving up a potential mine. Some assumptions
  may include
• The area is underlain by rock type X which isnt
  prospective.
• Comment How do you know? The map may be wrong or
  insufficiently detailed or covered by alluvial
  sediments. Perhaps that rock is prospective for
  some other commodity.
• The area has already been explored.
• Comment An area is seldom fully explored for all
  commodities. New models or commodities may make
  an area prospective again. Eg Cadia discovered
  early 1900s
• All prospective rocks are pegged by competitors.
• Comment When was the last check made on existing
  tenement plans? Tenements cost money to hold and
  are continually being relinquished. Have all the
  opportunities for joint venture or acquisition
  been explored?
• No existing ore body model fits the area.
• Comment Each mineral deposit is unique even
  though it may belong to a broad class of deposit.
  Beware of looking too closely for the last
  orebody rather than the next eg Kanowna Bell
  hosted in felsic volcanics rather than the
  greenstone (basalt) in Archean

6
Stages in Prospect Exploration

• Target Generation includes
• A review of all available information on the
  prospect, including government geol mapping and
  geophysical surveys, previous exploration and the
  known occurrence of minerals
• Preliminary interpretations of air photos and
  remote sensing data eg outcrop/regolith mapping
• Detailed geological mapping
• Detailed rock chip and soil sampling for
  geochemistry
• Detailed geochemical surveys
• Shallow pattern drilling for regolith or bedrock
  geochemistry (RAB, auger)
• Drilling aimed at increasing geological knowledge
• Target Drilling intersecting potential ore
• Resource Evaluation Drilling providing info on
  grade, tonnes and mining/metallurgical
  characteristics of potential ore body
• Feasibility Study assesses all factors
  geological, mining, environmental, political,
  economic, social and anything relevant to the
  decision to mine. High cost .

7
Stages in Prospect Exploration
8
Maximising Exploration Success
Not all prospects make it through to a mine. Most
will be discarded at the target generation or
drilling stages. Only a very few will make it to
the feasibility stage. The total number of
prospects that have to be generated to provide
one new mine discovery will generally be
large The graph shows 2 successful exploration
plays A C. Curve C must have been of a higher
quality land or been using a more successful
strategy. Curve B is a more typical prospect
wastage curve a failed exploration play
9
Maximising Exploration Success

• It is clear from the previous graph that there
  are only 2 ways to turn an unsuccessful
  exploration program into a successful one
• The exploration either has to get bigger ie
  increase the starting number of prospects
  generated. This is commonly the realm of big
  multi national companies.
• The explorationist has to get smarter! ie
  decrease the rate of prospect wastage and hence
  the slope of the exploration curve. This is
  generally the realm of small exploration
  companies with limited exploration budgets.
• A smart explorationist will generate the best
  quality prospects and test them in the most
  efficient and cost-effective manner, whilst
  maintaining a balance between generation and
  testing so as to maintain a continuous flow of
  directed activity leading to ore discovery. A
  good rollover rate of prospects is a sign of a
  healthy exploration program