Probabilistic mineral assessment research & development

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Strategy and approach

Our strategy for this project consists of two basic thrusts:

1. Improvements in the fundamental processes involved in the three-part assessment technique, and

2. Development of deposit models and simulation tests for deposits that have not yet been considered, namely bedded or layered metallic and non-metallic deposits and residual deposits derived from bedrock.

The first thrust is approached by three separate, but interrelated tasks:

• develop and implement improved economic filters that sort out which deposit has resources that are economic from those that are not;
• design and implement an updated, user friendly simulation program that is readily transportable.  The software is expected to replace previous versions currently that combine three-part assessment products to predict undiscovered resources;
• develop improved or possibly new methods for tract delineations for potential deposits based on modern GIS technology.

The second thrust is approached by a single task:

• investigate and develop practical models and new assessment approaches for important mineral resources that generally occur in sheet form (such as certain industrial mineral deposits and layered, platinum metals bearing ultramafic intrusions).
  

Tasks

Economic filters and assessment methods development

USGS mineral resource assessments provide estimates of the number and sizes of undiscovered mineral deposits in the form of a probability distribution. These estimates are made without regard to the economic feasibility of mining these deposits once discovered. Users of mineral resource assessments often require some level of analysis of the economic viability of these resources. Several tools are under development, known as economic filters, which would define the economic portion of estimated undiscovered resources based on various economic assumptions. Development of these tools has demonstrated that many factors beyond grade and tonnage help determine the economic potential of a deposit. Many of these factors are deposit or deposit-type specific, such as ore mineralogy, ore hardness, size of ore minerals, depth, distance from existing infrastructure, and determine the mining and mineral processing methods used and the magnitude of capital expenditures required. Other factors are external to deposits, such as mineral prices, taxation, country stability, and interest rates. The primary objective is to develop a set of economic tools that can be incorporated into the simulation process to estimate what portion of probability distribution of undiscovered resources that is economic. These tools will be developed in sequence, providing ever greater sophistication and reach, eventually covering all of the mineral deposit types considered by the Global and proposed National assessments.

Expanded and improved simulation programs for assessment

Existing software programs that predict the amount of undiscovered resources using products of three-step assessment approach are out-of-date and are difficult to modify. They need to be replaced with new generation of programs with greater flexibility that allow modifications and prepared in a programming script that are sufficiently transparent to allow future operators and users to understand and modify as needed. The objective of this task is to develop new, easily understood programs, either directly or by contract, that will provided estimates of undiscovered resources and their economic benefit for a wide range of both metal and industrial mineral deposit types.  Other sets of simulation script will be prepared for mineral assessments using new techniques were mineral resource assessment is not readily made using the three-step assessment approach.

Resources tracts preparation and assessment optimization and integration in GIS

Procedures in the preparation of tracts used for mineral resource assessment have not received rigorous study, particularly in light of recent advances in geospatial technologies. In addition, delineation guidelines associated with the development of mineral deposit density models can be improved using better prepared tracts. It is important to distinguish between tracts and deposits because tracts are always expected to have areas many times larger than the area of deposits. Delineation of tracts is also needed where no deposits of the type being assessed are recognized but permissive geology is present. In addition to information used prepare the tract boundaries; information within tracts is also used to estimate how many undiscovered deposits are likely. As such, the proper identification and accurate delineation of tracts is critical to the mineral resource assessment process. The overall objectives are to:

1. develop a number of geospatial methodologies and tools that will make the process of mineral resource assessment tract delineation less qualitative and more quantitative; however expert opinion will still be needed to compensate for the inevitable gaps in basic data
2. research approaches by which to include and integrate USGS mineral resource assessment products (primarily assessment tracts) in regional planning and development analyses.

Grade, tonnage and spatial modeling and assessment methods development

Developing new or refining appropriate, existing mineral-deposit grade, tonnage, and spatial models is a necessary building block in three-part probabilistic assessing mineral deposit resources. Reductions in the number of inaccuracies and their uncertainties in probabilistic mineral resource assessments occur with consistent application of operational rules when defining deposits. For example, two operational rules are used to define deposits when constructing grade and tonnage models for porphyry copper deposits. First, only those occurrences whose reported resources are well-defined in three dimensions are included as deposits in the model; occurrences with partially delineated resources are considered prospects. Second, resources associated with all well-characterized occurrences within 2 kilometers of each other are aggregated into a single deposit for modeling purposes. Some economically important metallic and industrial mineral deposits occur in sheet-like form - either bedded or stratiform. The shape of these deposits can be difficult to assess using the three-part assessment approach because the deposits can be unbounded (although resources are reported and are produced, the deposits are open laterally or at depth). In addition, aggregation rules used to define the extent of deposits to be included in models can be ambiguous when applied to sheet-like deposits. However, these sheet-like deposits, when geologically bounded and continue, can have tonnage that may be estimated using footprint-tonnage regression. Our objective is to develop and evaluate several approaches to assess sheet-like deposits that will produce results that express uncertainty in the estimate and can be compared to the output from previous quantitative estimates based on grade, tonnage, and undiscovered deposit distributions. We will need to develop operational rules that define a deposit and the discovered and undiscovered resources they contain.