Page 20 - Introduction to Mineral Exploration

1

Ore, Mineral Economics,

and Mineral Exploration

Charles J. Moon and Anthony M. Evans

1.1 INTRODUCTION deposit can be called a mineral resource.”
“Mineral Resources are subdivided, in order of
A large economic mineral deposit, e.g. 200 Mt increasing geological confidence, into Inferred,
2
underlying an area of 2 km , is minute in com- Indicated, and Measured categories.” A more
parison with the Earth’s crust and in most complete explanation is given in section 10.4.1.
countries the easily found deposits cropping The JORC Code then explains that “an ore
out at the surface have nearly all been found. reserve is the economically mineable part of
The deposits for which we now search are a Measured or Indicated Mineral Resource.
largely concealed by weathered and leached It includes diluting materials and allowances
outcrops, drift, soil, or some other cover, and for losses that may occur when the material
sophisticated exploration methods are required is mined. Appropriate assessments, which may
to find them. The target material is referred include feasibility studies (see section 11.4),
to as a mineral deposit, unless we use a more have been carried out, and include consid-
specific term such as coal, gas, oil, or water. eration of and modification by realistically
Mineral deposits contain mineral resources. assumed mining, metallurgical, economic,
What sort of mineral deposit should we seek? marketing, legal, environmental, social, and
To answer this question it is necessary to have governmental factors. These assessments
some understanding of mineral economics. demonstrate at the time of reporting that
extraction could reasonably be justified.” “Ore
Reserves are sub-divided in order of increasing
1.2 MINERAL ECONOMICS confidence into Probable Ore Reserves and
Proved Ore Reserves.”
“The term ‘economic’ implies that extrac-
1.2.1 Ore
tion of the ore reserve has been established
Ore is a word used to prefix reserves or body but or analytically demonstrated to be viable
the term is often misused to refer to any or all and justifiable under reasonable investment
in situ mineralisation. The Australasian Joint assumptions. The term ore reserve need not
Ore Reserves Committee (2003) in its code, the necessarily signify that extraction facilities are
JORC Code, leads into the description of ore in place or operative or that all governmental
reserves in the following way: “When the loca- approvals have been received. It does signify
tion, quantity, grade, geological characteristics that there are reasonable expectations of such
and continuity of mineralisation are known, approvals.” An orebody will be the portion of
and there is a concentration or occurrence a mineralized envelope within which ore
of the material of intrinsic economic interest reserves have been defined.
in or on the Earth’s crust in such form and Ore minerals are those metallic minerals,
quantity that there are reasonable prospects e.g. galena, sphalerite, chalcopyrite, that form
for eventual economic extraction, then this the economic portion of the mineral deposit.