Open Pit Mine - Planning and Design-3rd Edition

Open Pit Mine - Planning and Design-3rd Edition

(Parte 3 de 7)

Profits <0 (1.5)

This, needless to say, is unfavorable for all concerned (the employees, the company, and the country or nation). For the mining engineer (student or practicing) reading this book, the personal meaning of ore is

Ore = Profits = Jobs (1.6)

The use of the mathematical equivalence symbol simply says that 'ore' is equivalent to 'profits' which is equivalent to 'jobs'. Hence one important meaning of 'ore' to us in the minerals business is jobs. Probably this simple practical definition is more easily remembered than those offered earlier. The remainder of the book is intended to provide the engineer with tools to perform even better in an increasingly competitive world.

1.1.2 Some important definitions

The exploration, development, and production stages of a mineral deposit (Banfield & Havard, 1975) are defined as:

Exploration: The search for a mineral deposit (prospecting) and the subsequent investigation of any deposit found until an orebody, if such exists, has been established.

Development: Work done on a mineral deposit, after exploration has disclosed ore in sufficient quantity and quality to justify extraction, in order to make the ore available for mining.

Production: The mining of ores, and as required, the subsequent processing into products ready for marketing.

It is essential that the various terms used to describe the nature, size and tenor of the deposit be very carefully selected and then used within the limits of well recognized and accepted definitions.

Over the years a number of attempts have been made to provide a set of universally accepted definitions for the most important terms. These definitions have evolved somewhat as the technology used to investigate and evaluate orebodies has changed. On February 24, 1991, the report, 'A Guide for Reporting Exploration Information, Resources and Reserves' prepared by Working Party No. 79 - 'Ore Reserves Definition' of the Society of Mining, Metallurgy and Exploration (SME), was delivered to the SME Board of Directors (SME,

Mine planning 3

1991). This report was subsequently published for discussion. In this section, the 'Definitions' and 'Report Terminology' portions of their report (SME, 1991) are included. The interested reader is encouraged to consult the given reference for the detailed guidelines. The definitions presented are tied closely to the sequential relationship between exploration information, resources and reserves shown in Figure 1.1.

With an increase in geological knowledge, the exploration information may become sufficient to calculate a resource. When economic information increases it may be possible to convert a portion of the resource to a reserve. The double arrows between reserves and resources in Figure 1.1 indicate that changes due to any number of factors may cause material to move from one category to another.

Definitions Exploration information. Information that results from activities designed to locate economic deposits and to establish the size, composition, shape and grade of these deposits. Exploration methods include geological, geochemical, and geophysical surveys, drill holes, trial pits and surface underground openings.

Resource. A concentration of naturally occurring solid, liquid or gaseous material in or on the Earth's crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible. Location, grade, quality, and quantity are known or estimated from specific geological evidence. To reflect varying degrees of geological certainty, resources can be subdivided into measured, indicated, and inferred.

- Measured. Quantity is computed from dimensions revealed in outcrops, trenches, workings or drill holes; grade and/or quality are computed from the result of detailed sampling. The sites for inspection, sampling and measurement are spaced so closely and the geological character is so well defined that size, shape, depth and mineral content of the resource are well established.

CD 'S ° "g <D Sf ë 1) O ® ç CD S = g lì 8* ~ O) "O ° 5 £ Ö c

Exploration Information

Resources Reserves Inferred

Indicated <1 • Probable

Measured < • Proven

Economic, mining, metallurgical, marketing environmental, social and governmental factors may cause material to move between resources and reserves

Figure 1.1. The relationship between exploration information, resources and reserves (SME, 1991).

4 Open pit initie planning and design: Fundamentals

- Indicated. Quantity and grade and/or quality are computed from information similar to that used for measured resources, but the sites for inspection, sampling, and measurements are farther apart or are otherwise less adequately spaced. The degree of assurance, although lower than that for measured resources, is high enough to assume geological continuity between points of observation.

- Inferred. Estimates are based on geological evidence and assumed continuity in which there is less confidence than for measured and/or indicated resources. Inferred resources may or may not be supported by samples or measurements but the inference must be supported by reasonable geo-scientific (geological, geochemical, geophysical, or other) data.

Reseive. A reserve is that part of the resource that meets minimum physical and chemical criteria related to the specified mining and production practices, including those for grade, quality, thickness and depth; and can be reasonably assumed to be economically and legally extracted or produced at the time of determination. The feasibility of the specified mining and production practices must have been demonstrated or can be reasonably assumed on the basis of tests and measurements. The term reserves need not signify that extraction facilities are in place and operative.

The term economic implies that profitable extraction or production under defined investment assumptions has been established or analytically demonstrated. The assumptions made must be reasonable including assumptions concerning the prices and costs that will prevail during the life of the project.

The term 'legally' does not imply that all permits needed for mining and processing have been obtained or that other legal issues have been completely resolved. However, for a reserve to exist, there should not be any significant uncertainty concerning issuance of these permits or resolution of legal issues. Reserves relate to resources as follows:

- Proven reserve. That part of a measured resource that satisfies the conditions to be classified as a reserve.

- Probable reserve. That part of an indicated resources that satisfies the conditions to be classified as a reserve.

It should be stated whether the reserve estimate is of in-place material or of recoverable material. Any in-place estimate should be qualified to show the anticipated losses resulting from mining methods and beneficiation or preparation.

Reporting terminology The following terms should be used for reporting exploration information, resources and reserves:

1. Exploration information. Terms such as 'deposit' or 'mineralization' are appropriate for reporting exploration information. Terms such as 'ore,' 'reserve,' and other terms that imply that economic extraction or production has been demonstrated, should not be used.

2. Resource. A resource can be subdivided into three categories: (a) Measured resource;

(b) Indicated resource; (c) Inferred resource.

The term 'resource' is recommended over the terms 'mineral resource, identified resource' and 'in situ resource.' 'Resource' as defined herein includes 'identified resource,' but excludes 'undiscovered resource' of the United States Bureau of Mines (USBM) and United

Mine planning 5

States Geological Survey (USGS) classification scheme. The 'undiscovered resource' classification is used by public planning agencies and is not appropriate for use in commercial ventures.

3. Reserve. A reserve can be subdivided into two categories: (a) Probable reserve; (b) Proven reserve.

The term 'reserve' is recommended over the terms 'ore reserve,' 'minable reserve' or 'recoverable reserve.'

The terms 'measured reserve' and 'indicated reserve,' generally equivalent to 'proven reserve' and 'probable reserve,' respectively, are not part of this classification scheme and should not be used. The terms 'measured,' 'indicated' and 'inferred' qualify resources and reflect only differences in geological confidence. The terms 'proven' and 'probable' qualify reserves and reflect a high level of economic confidence as well as differences in geological confidence.

The terms 'possible reserve' and 'inferred reserve' are not part of this classification scheme. Material described by these terms lacks the requisite degree of assurance to be reported as a reserve.

The term 'ore' should be used only for material that meets the requirements to be a reserve. It is recommended that proven and probable reserves be reported separately. Where the term reserve is used without the modifiers proven or probable, it is considered to be the total of proven and probable reserves.

1.2 MINE DEVELOPMENT PHASES

The mineral supply process is shown diagrammatically in Figure 1.2. As can be seen a positive change in the market place creates a new or increased demand for a mineral product.

In response to the demand, financial resources are applied in an exploration phase resulting in the discovery and delineation of deposits. Through increases in price and/or advances in technology, previously located deposits may become interesting. These deposits must then be thoroughly evaluated regarding their economic attractiveness. This evaluation process will be termed the 'planning phase' of a project (Lee, 1984). The conclusion of this phase will be the preparation of a feasibility report. Based upon this, the decision will be made as to whether or not to proceed. If the decision is 'go', then the development of the mine and concentrating facilities is undertaken. This is called the implementation, investment, or design and construction phase. Finally there is the production or operational phase during which the mineral is mined and processed. The result is a product to be sold in the marketplace. The entrance of the mining engineer into this process begins at the planning phase and continues through the production phase. Figure 1.3 is a time line showing the relationship of the different phases and their stages.

The implementation phase consists of two stages (Lee, 1984). The design and construction stage includes the design, procurement and construction activities. Since it is the period of major cash flow for the project, economies generally result by keeping the time frame to a realistic minimum. The second stage is commissioning. This is the trial operation of the individual components to integrate them into an operating system and ensure their readiness

6 Open pit initie planning and design: Fundamentals

Ejjploratiom Discovery

Delineation / Demand for

.mineral product

Changes ins market e \ a> u

„Occurrence of ORE deposit

DeveSojj mine extraction facilities

Mine and process

Figure 1.2. Diagrammatic representation of the mineral supply process (McKenzie, 1980).

Figure 1.3. Relative ability to influence costs (Lee, 1984).

for startup. It is conducted without feedstock or raw materials. Frequently the demands and costs of the commissioning period are underestimated.

The production phase also has two stages (Lee, 1984). The startup stage commences at the moment that feed is delivered to the plant with the express intention of transforming it into product. Startup normally ends when the quantity and quality of the product is sustainable at the desired level. Operation commences at the end of the startup stage.

Mine planning 13

As can be seen in Figure 1.3, and as indicated by Lee (1984),

or fiscal disaster into a developing project, that is inherent in the planning phase

the planning phase offers the greatest opportunity to minimize the capital and operating costs of the ultimate project, while maximizing the operability and profitability of the venture. But the opposite is also true: no phase of the project contains the potential for instilling technical

At the start of the conceptual study, there is a relatively unlimited ability to influence the cost of the emerging project. As decisions are made, correctly or otherwise, during the balance of the planning phase, the opportunity to influence the cost of the job diminishes rapidly.

The ability to influence the cost of the project diminishes further as more decisions are made during the design stage. At the end of the construction period there is essentially no opportunity to influence costs.

The remainder of this chapter will focus on the activities conducted within the planning stage.

1.3 AN INITIAL DATA COLLECTION CHECKLIST

In the initial planning stages for any new project there are a great number of factors of rather diverse types requiring consideration. Some of these factors can be easily addressed, whereas others will require in-depth study. To prevent forgetting factors, checklist are often of great value. Included below are the items from a 'Field Work Program Checklist for New Properties' developed by Halls (1975). Student engineers will find many of the items on this checklist of relevance when preparing mine design reports. Checklist items (Halls, 1975)

1. Topography (a) USGS maps (b) Special aerial or land survey

Establish survey control stations Contour

2. Climatic conditions (a) Altitude (b) Temperatures

Extremes Monthly averages

(c) Precipitation

Average annual precipitation Average monthly rainfall Average monthly snowfall Run-off

Normal Flood Slides - snow and mud

(d) Wind

Maximum recorded Prevailing direction Hurricanes, tornados, cyclones, etc.

14 Open pit initie planning and design: Fundamentals

(e) Humidity Effect on installations, i.e. electrical motors, etc.

(f) Dust (g) Fog and cloud conditions 3. Water - potable and process (a) Sources

Streams Lakes Wells

(b) Availability

Ownership Water rights Cost

(c) Quantities

Monthly availability Flow rates Drought or flood conditions Possible dam locations

(d) Quality Present sample

Possibility of quality change in upstream source water Effect of contamination on downstream users

(e) Sewage disposal method 4. Geologic structure (a) Within mine area (b) Surrounding areas (c) Dam locations (d) Earthquakes (e) Effect on pit slopes Maximum predicted slopes

(f) Estimate on foundation conditions 5. Mine water as determined by prospect holes (a) Depth (b) Quantity (c) Method of drainage 6. Surface (a) Vegetation

Type Method of clearing Local costs for clearing

(b) Unusual conditions

Extra heavy timber growth Muskeg

Lakes

Stream diversions Gravel deposits

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7. Rock type - overburden and ore (a) Submit sample for drillability test (b) Observe fragmentation features Hardness

Degree of weathering Cleavage and fracture planes Suitability for road surface

8. Locations for concentrator - factors to consider for optimum location (a) Mine location

Haul uphill or downhill (b) Site preparation Amount of cut and/or fill

(c) Process water

Gravity flow or pumping (d) Tailings disposal Gravity flow or pumping

(Parte 3 de 7)

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