Module 3 Overview

Hello and welcome to another module of Introduction to Mining Engineering. I'm Dr. Shekhar Bhattacharyya, your instructor.

Today, we'll delve into the early stages of the mining lifecycle, focusing on exploration and reserve estimation. By the end of this module, you'll understand how we define mineral resources, estimate reserves, and determine economic parameters such as cut-off grade and stripping ratio.

First, let's distinguish between prospecting and exploration.

Prospecting is largely performed by geoscientists. Its purpose is to locate mineral concentrations. Once a potential deposit has been identified, exploration follows. Mining engineers often take the lead in designing the sampling and drilling programs required to evaluate the deposit.

In this module, you'll be introduced to:

• The goals and methods of an exploration program
• The differences between core drilling and reverse-circulation drilling
• How to develop a sampling plan that ensures geologic and grade continuity
• The distinction between mineral resources and mineral reserves
• Resource estimation methods, including polygonal, triangular, and inverse-distance weighting techniques
• The calculation of cut-off grade and stripping ratio for economic analysis

Once prospecting has identified a potential deposit, the objective of exploration is to define its shape, size, orientation, depth, grade, and geotechnical characteristics. Exploration programs often include metallurgical and geophysical testing to assess ore quality and structural integrity. Reliable information comes from careful sampling and well-designed drilling programs.

Two main drilling methods are commonly used.

The first is core drilling, which recovers intact rock cores. Core drilling preserves geologic structures and is ideal for geotechnical analysis.

The second is reverse-circulation drilling (sometimes referred to as rotary percussion drilling). This method produces small rock chips, or cuttings, and is generally less expensive than core drilling. However, because no intact core is recovered, valuable structural information is lost. Although core drilling is more expensive, it provides invaluable geologic detail. Reverse-circulation drilling is faster and more cost-effective for initial grade estimation.

One of the challenges in exploration is designing an effective sampling pattern. If drill-hole spacing is too wide or too regular, important mineralized zones may be missed or grade continuity may be poorly estimated. Good practice involves spacing drill holes according to the minimum mineable dimensions of the deposit.

Now let's clarify some key terminology.

A mineral resource is a naturally occurring concentration of material that has reasonable prospects for economic extraction. Mineral resources are classified into three categories:

• Measured Resources – High confidence, supported by dense and reliable sampling
• Indicated Resources – Moderate confidence, where sampling density is sufficient to support a reasonable interpretation
• Inferred Resources – Lower confidence, based on more limited geologic information

A mineral reserve is the portion of a mineral resource that can be economically mined under current conditions.

Reserve classifications include:

• Proven Reserves – Derived primarily from measured resources and associated with the highest level of confidence
• Probable Reserves – Typically derived from indicated resources and associated with moderate confidence

Proven reserves are generally the most valuable category for mine planning and investor confidence. These legal and reporting distinctions are important for regulatory compliance and financial transparency.

Once resources are defined, reserves can be estimated using spatial interpolation methods.

One common approach is the polygonal or triangular method, which divides a deposit into planar blocks using triangles or Voronoi polygons around drill holes. Each drill hole's data is weighted according to the area associated with that hole.

Another commonly used method is inverse-distance weighting (IDW). This technique estimates values such as grade or thickness at unsampled locations using weighted averages, where nearby samples have greater influence than distant samples.

These methods account for the area of influence of each sample, helping ensure that estimated averages reflect the variability of the deposit. You should be able to calculate weighted average grade and thickness using these approaches. These techniques form the foundation of resource estimation before economic reserves are defined.

There are many additional geostatistical methods available for resource and reserve estimation. These more advanced methods are typically studied in upper-level mining engineering courses.

Once a resource estimate has been completed, we must determine how much of the resource can be economically recovered. Two key metrics support this analysis: cut-off grade and stripping ratio.

The cut-off grade is the minimum ore grade required to cover mining, processing, and operating costs. Material below this threshold is typically classified as waste or left unmined.

The stripping ratio is the ratio of waste material removed to ore extracted in a surface mining operation.

For tabular, flat-lying deposits, engineers calculate a maximum, or break-even, stripping ratio to determine economic pit limits.

For dipping deposits, engineers may use the instantaneous stripping ratio and the maximum allowable stripping ratio. As pit depth increases, waste volume often grows more rapidly than ore volume, causing the stripping ratio to increase. Once the stripping ratio exceeds the break-even limit, deeper portions of the deposit may become uneconomic to mine. These calculations are critical for determining pit expansion potential and ultimate mining limits.

To summarize this module:

• Prospecting identifies potential mineral concentrations.
• Exploration defines those concentrations in detail.
• Well-designed drilling and sampling programs improve geologic understanding and reduce uncertainty.
• Mineral resources are classified as measured, indicated, or inferred.
• Mineral reserves are classified as proven or probable.
• Resource estimates commonly rely on polygonal, triangular, and inverse-distance weighting methods.
• Cut-off grade and stripping ratio help determine which portions of a resource can be mined economically.

Thank you for your attention. Please review the module notes and complete the assignments before proceeding to the next module.

I will see you again soon with another module of Introduction to Mining Engineering. Until then, keep learning and stay safe.