Mining Goes Digital – Mueller et al. (Eds)
© 2019 Taylor & Francis Group, London, ISBN 978-0-367-33604-2
115
Optimal drill hole spacing for resource classification
Marek Nowak
SRK Consulting Canada Inc., Vancouver, BC, Canada
Oy Leuangthong
SRK Consulting Canada Inc., Toronto, ON, Canada
ABSTRACT: Regulatory bodies around the world have relied on similar definitions for
mineral resource categories, and subdivide mineral resources in order of increasing geological
confidence: Inferred, Indicated and Measured. Major investment and development decisions
are based on a correct assignment of a resource to a proper category. The progression to
mineral reserves reporting requires at least the categorization of Indicated and/or Measured
resources. As such, the assignment of a mineral resource to an Indicated category should be
recognized as a necessary step to advance towards the feasibility of a project.
Allocation of mineral resource categories often relies on some geostatistical tools, of which
drill hole spacing is perhaps most common. This paper looks at procedures to determine the
optimal drill hole spacing required for allocation of a portion of resources to an Indicated
category in metal deposits. These procedures are differentiated into two main groups based
on their simplicity and stage of application: (1) general assessment of adequate drill hole
spacing; and (2) local assessment of uncertainty on estimated grade within large panels representing monthly or quarterly production. At an early exploration stage general assessment
of optimal drill hole spacing for an assignment to an Indicated category is quite adequate.
On the other hand, at a pre-feasibility stage simulation studies represent the best tool for
resource categorization. Practical examples from a case study the authors have worked on
will be presented.
1 INTRODUCTION
Mineral resource estimation models are always sub-divided in order of increasing geological
confidence into Inferred, Indicated, and Measured categories. The definitions of mineral
resource categories are very similar between the Canadian Institute of Mining (CIM), The
Australasian Code for Reporting of Mineral Resources and Ore Reserves (JORC), and the
South African Code for Reporting of Mineral Resources and Mineral Reserves (SAMREC).
The established standards for reporting on resource categories are based on a Qualified Person’s (QP) assessment of geological and grade continuities and, in general, are often based on
the QP’s subjective assessment of confidence on the estimated tonnage and grade.
Important, and often costly, investment decisions rely on this assignment of resources
into different classification categories. At an early exploration stage, resources are usually
allocated to an Inferred category. With each additional drill campaign, the portions of the
Inferred category resources can be upgraded to Indicated or Measured categories. Once a
resource has been assigned to an Indicated or higher category, it has the potential to be converted to a Probable Reserve. The conversion to the reserves is not possible for an Inferred
category resource. Therefore, the assignment of a mineral resource to at least an Indicated
category is a necessary step to advance towards the feasibility of a project and eventually
towards mine development and construction.
© 2019 Taylor & Francis Group, London, ISBN 978-0-367-33604-2
115
Optimal drill hole spacing for resource classification
Marek Nowak
SRK Consulting Canada Inc., Vancouver, BC, Canada
Oy Leuangthong
SRK Consulting Canada Inc., Toronto, ON, Canada
ABSTRACT: Regulatory bodies around the world have relied on similar definitions for
mineral resource categories, and subdivide mineral resources in order of increasing geological
confidence: Inferred, Indicated and Measured. Major investment and development decisions
are based on a correct assignment of a resource to a proper category. The progression to
mineral reserves reporting requires at least the categorization of Indicated and/or Measured
resources. As such, the assignment of a mineral resource to an Indicated category should be
recognized as a necessary step to advance towards the feasibility of a project.
Allocation of mineral resource categories often relies on some geostatistical tools, of which
drill hole spacing is perhaps most common. This paper looks at procedures to determine the
optimal drill hole spacing required for allocation of a portion of resources to an Indicated
category in metal deposits. These procedures are differentiated into two main groups based
on their simplicity and stage of application: (1) general assessment of adequate drill hole
spacing; and (2) local assessment of uncertainty on estimated grade within large panels representing monthly or quarterly production. At an early exploration stage general assessment
of optimal drill hole spacing for an assignment to an Indicated category is quite adequate.
On the other hand, at a pre-feasibility stage simulation studies represent the best tool for
resource categorization. Practical examples from a case study the authors have worked on
will be presented.
1 INTRODUCTION
Mineral resource estimation models are always sub-divided in order of increasing geological
confidence into Inferred, Indicated, and Measured categories. The definitions of mineral
resource categories are very similar between the Canadian Institute of Mining (CIM), The
Australasian Code for Reporting of Mineral Resources and Ore Reserves (JORC), and the
South African Code for Reporting of Mineral Resources and Mineral Reserves (SAMREC).
The established standards for reporting on resource categories are based on a Qualified Person’s (QP) assessment of geological and grade continuities and, in general, are often based on
the QP’s subjective assessment of confidence on the estimated tonnage and grade.
Important, and often costly, investment decisions rely on this assignment of resources
into different classification categories. At an early exploration stage, resources are usually
allocated to an Inferred category. With each additional drill campaign, the portions of the
Inferred category resources can be upgraded to Indicated or Measured categories. Once a
resource has been assigned to an Indicated or higher category, it has the potential to be converted to a Probable Reserve. The conversion to the reserves is not possible for an Inferred
category resource. Therefore, the assignment of a mineral resource to at least an Indicated
category is a necessary step to advance towards the feasibility of a project and eventually
towards mine development and construction.