Real-Time Targeting with Quality Structural Data- Bringing QAQC to Oriented Core Drilling

Core orientation

Introduction:

Oriented core drilling methods have rapidly evolved over the last several years, leading to a recent uptick in use and multiple case studies where proper use of the tool leads to discovery. Modern orientation tools utilize solid-state accelerometer sensors to reliably determine and mark the position of the downward acceleration vector of gravity on core. A line is drawn down the length of the core at the location of the orientation mark and geologic structures are measured relative to the orientation line. This allows precision 3D modelling of planar and linear structural features, and most importantly, real-time mapping of structures that control mineralization. While modern orientation tools are proven to be accurate and reliable, many users have experienced frustration and a lack of confidence in the resulting structural data because there isn’t an industry accepted method to manage quality of the orientation process. The potential of this exploration tool can only be realized once geologists are accountable for managing the quality of the orientation process.

Structural Data QAQC:

Seasoned exploration geologists may remember the days when there was a similar lack of confidence in the integrity of assay data. Along with the introduction of sample blanks and standards came the addition of “QAQC” to the lexicon of the exploration geologist. Quality-assurance/Quality-control (QAQC) brought validation and confidence to assay data. This has been revolutionary because geochemical data typically is the primary vector for targeting mineralization and is critical for resource estimates. Structural controls on mineralization are the next priority vectors, yet there’s no industry standard for implementing QAQC to structural data collection and synthesis. Since both assay and structural data are typically the two greatest factors considered for targeting, there needs to be established QAQC protocol for both.

Managing Errors:

The most reliable aspect of modern accelerometer-based orientation tools is that when used correctly, they always orient the core barrel for every run of core. This means that the greatest chance for error comes during subsequent steps of marking the core and collecting structural measurements. The three sources of error which must be understood and actively mitigated during oriented core drilling are:

  • Creating the orientation mark
  • Drawing the orientation line
  • Collecting structural data

These errors are cumulative over every run of core but are not cumulative over multiple runs of core. Every new core run is essentially a “reset” when using modern accelerometer-based orientation tools.

The simplest and most effective way to bring QAQC to core orientation is by creating an orientation log during the drilling process. A recommended orientation log format is provided in Table 1 below.

Table 1: Recommended orientation log format

HoleID
Mark Depth_ft
From_ft
To_ft
Mark Quality
Interval Quality
Lock Angle
Comments
Rotation Angle
OM used to correct
Logger

The orientation log provides the means for rating the quality of the orientation mark and line, provides a record for lock-angle data (the angular distance between orientation lines from different runs of core), documents errors, and allows correction for erroneous intervals of orientation line. The log is continuous over the entire hole with unique records indicating where there is and isn’t an orientation line. The log is simple to construct and provides a permanent record that can be reviewed and modified at any time.

Lock angles (Table 1) are the only test that can validate the quality of an orientation line. The logic is based on the fact that an orientation line drawn from an orientation mark will have a very low probability of randomly lining-up with an orientation mark from an adjacent run of core. Structural measurements collected within lock-angle-validated intervals of orientation line can then be assigned scaled numeric quality attributes (Table 1- Interval Quality), and good quality data can be prioritized for plotting and interpretation.

The main objectives for orientation QAQC is to ensure that the quality of oriented structural data is known, and to prioritize high-quality data for geologic modelling and interpretation. Since an orientation log does not exist for most past and current oriented drill programs, qualifying resultant structural data is typically not an option. With no documented QAQC, un-locked (and thus un-validated) core intervals must be considered “neutral”. This signifies that the quality is undeterminable (i.e. could be good or could be bad). The end-result is commonly uninterpretable or misleading stereonet plots due to the fact that erroneous data cannot be easily filtered-out prior to plotting. That-being-said, the neutral data should not be discarded, but should instead be plotted on stereonets so significant structural domain patterns or patterns of error can be identified.

Starting a New Oriented Core Program Off on the Right Foot:

The best way forward is to quickly establish QAQC best-practices at the beginning of any oriented drill program. This must be backed-up by proper training and supervision of all involved with the orientation. QC is management, QA means data, and not to forget, proper QC involves constant review of QA data. Those involved in project planning need to determine what the goals are for oriented core drilling, and what level of precision is needed to reach the desired goals. The next step is creating an SOP for orientation that includes QAQC. The steps below outline the recommended workflow from orientation, to real-time targeting of structural controls on mineralization with quality data.

  • Understand the sources of error and actively mitigate them
  • Create an orientation log
  • Correct erroneous data
  • Create a query-able structural database
  • Assign quality ratings to structural data
  • Join structural data with assay data
  • Query the structural database
  • Plot high-quality structural data on pole to plane stereonets right away!
  • Identify structural controls on mineralization
  • Import queries for structural controls into the 3D model
  • Real-time targeting

Summary:

When used correctly, oriented core is an incredibly powerful exploration tool in all precious and base metal deposit types.  Whether its fabrics, lithological contacts, or cross-cutting features; there’s always an element of structural control on mineralization. Our focus is on maximizing the potential of modern orientation tools by getting geologists to take responsibility for the integrity of the resulting structural data. Engineers realize the importance of data QAQC and typically control and manage the process of drill data capture from start to finish. This is because they care about the integrity of their data. Geologists need to do the same.

Quality controls on oriented core drilling programs result in validation of data quality, more orientation, and a higher percentage of high-quality structural data. Once the quality protocols are in place, the sky’s the limit. With a well-classified structural database an almost endless amount of queries can be devised to reveal controls on mineralization and identify targets. In our experience, clients that implement quality controls and evolve their oriented core programs to the stage of real-time structural analysis with quality data never look back. Over time, as deposits increasingly become “blind”, high-quality oriented structural data will increasingly be a major determining factor in project breakthroughs and new discoveries.

About the author, Chris Brown

Chris Brown has 21 years of experience in exploration and has been working with oriented core for 8 years. His interest in oriented core is fueled by a drive to make new discoveries using the best technology available. Since his approach is inspired by the perspective of an exploration geologist, the main objective is always finding the most effective way to target controls on mineralization in real-time.
Oriented Targeting Solutions LLC, Reno, Nevada
cbrown@orientedcore.com

1 Comment

  1. Danie Sandova on 06/20/2018 at 9:32 AM

    Great article

Leave a Comment