Map Scale Effects on Estimating the Number of Undiscovered Mineral Deposits |
| |
| Authors: | Donald A Singer W David Menzie |
| |
| Institution: | (1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA;(2) U.S. Geological Survey, 12201 Sunrise Valley Dr, Reston, VA 20192, USA |
| |
| Abstract: | Estimates of numbers of undiscovered mineral deposits, fundamental to assessing mineral resources, are affected by map scale.
Where consistently defined deposits of a particular type are estimated, spatial and frequency distributions of deposits are
linked in that some frequency distributions can be generated by processes randomly in space whereas others are generated by
processes suggesting clustering in space. Possible spatial distributions of mineral deposits and their related frequency distributions
are affected by map scale and associated inclusions of non-permissive or covered geological settings. More generalized map
scales are more likely to cause inclusion of geologic settings that are not really permissive for the deposit type, or that
include unreported cover over permissive areas, resulting in the appearance of deposit clustering. Thus, overly generalized
map scales can cause deposits to appear clustered. We propose a model that captures the effects of map scale and the related
inclusion of non-permissive geologic settings on numbers of deposits estimates, the zero-inflated Poisson distribution. Effects
of map scale as represented by the zero-inflated Poisson distribution suggest that the appearance of deposit clustering should
diminish as mapping becomes more detailed because the number of inflated zeros would decrease with more detailed maps. Based
on observed worldwide relationships between map scale and areas permissive for deposit types, mapping at a scale with twice
the detail should cut permissive area size of a porphyry copper tract to 29% and a volcanic-hosted massive sulfide tract to
50% of their original sizes. Thus some direct benefits of mapping an area at a more detailed scale are indicated by significant
reductions in areas permissive for deposit types, increased deposit density and, as a consequence, reduced uncertainty in
the estimate of number of undiscovered deposits. Exploration enterprises benefit from reduced areas requiring detailed and
expensive exploration, and land-use planners benefit from reduced areas of concern. |
| |
| Keywords: | Mineral resource assessments mineral deposit density zero-inflated Poisson mapping benefits |
| 本文献已被 SpringerLink 等数据库收录！ |
|
