Deep Exploration Technologies CRC: Uncovering the Future

Deep Exploration Technologies CRC: Uncovering the Future

Prospecting at DepthWhat compromises are you willing to make?

David GilesProgram 3 Leader DET CRCSchool of Earth and Environmental SciencesThe University of Adelaide

Thesis

• We don’t understand complex mineral systems nearly as well as we think we do

• You can’t predict the unpredictable • You can only map and sample the systems at a detail

appropriate to the system and to your needs• Where prospective rocks are exposed this process is called

‘prospecting’ • Prospecting can be very effective – low cost – drives and

informs the exploration cycle – mitigates risk• Where prospective rocks are covered we don’t yet have an

equivalent• Increased sample density requires reduced cost per sample• What compromises are acceptable?• DET CRC research aims to address this issue

Ore deposits (and associated fault networks) tend to have a fractal distribution.Scale independent distribution at the length scales appropriate to exploration.

Ore deposits tend to have a fractal distributionScale independent distribution at the length scales appropriate to exploration

Global porphyrydeposits (234)

Dead sea riftearthquakes

From: Seismicity parameters of Seismogenic Zones (Avi Shapira and Abraham Hofstetter) www.gii.co.il/heb/ Teken/seismicity-rprt.htm

Size vs frequency gives straight line in log-log

Self Organized CriticalSystems

Inherently unpredictable

http://www.gii.co.il/heb/Teken/seismicity-rprt.htm



This analogy does not sound very encouraging to a mineral explorer.

Because we have to do more than find the fault – we have to effectively predict the earthquake.

However there are a number of reasons for us to be encouraged:

1. We can employ methods of pattern recognition informed by experience (geologists intuition), for example…

Ore deposits are distributed in

clusters both in space…

…and in time…

Hodkiewicz et al, 2005, AJES 52: 831-841 …and are focused in zones of structural complexity

There are a number of reasons for us to be encouraged:

2. We don’t have to predict into the future. We are making a spatial prediction on past events and as such WE DON’T HAVE TO PREDICT WE CAN OBSERVE and MEASURE in order to build a picture of the PATTERN.

IN GEOLOGY WE CALL THAT MAPPING and SAMPLING

400km

200km

Semi-regular sampling at 80km intervals granite

basalt

limestone

shale siltstone

sandstone

400km

200km


basalt

limestone

shale siltstone

sandstone

400km

200km


basalt

limestone

shale siltstone

sandstone

400km

200km


basalt

limestone

shale siltstone

sandstone

400km

200km


basalt

limestone

shale siltstone

sandstone

400km

200km

The full complexity revealed!

There are a number of reasons for us to be encouraged:

3. We can use our understanding of mineral systems and secondary dispersion processes to markedly increase the size of the target FOOTPRINT. (the analogy is identifying the epicentre of an earthquake by measuring the intensity of damage at the surface)

In deposit sampling we are interested in constraining the distribution of grade and mineralogy (deleterious materials, mining parameters…) at a scale appropriate to mining (~5m).

In exploration sampling we are interested in any rock property (geochemistry, mineralogy, texture, petrophysics) that will allow us to reconstruct the mineral system (ie recognise the pattern) at a scale that will allow us to make the next targeting decision.

murphygeological.com

5km

Alunite alteration associated with high

sulphidation epithermal systems in northern Chile

www.magellanminerals.com

PROSPECTINGWhy we love it…

• Low cost• Maps system• Informs decisions• Drives progress through

exploration cycle

www.orezone.com

• At depth no prospecting phase!

• Fabulous large scale datasets but…

• Often single data set anomaly

• Deep hole – high cost – big risk – long lead time to validation

• Lots of false positives

Prospecting at depth

At present we have sparse sampling coupled with regional geophysical data (mostly potential fields)

Geophysics lends itself to structural interpretation (equivalent of identifying the fault corridor for earthquake prediction).

But huge ambiguity about detail of structures, rock types, alteration, elemental geochemistry (particularly if these variables do not influence the geophysical signature).

The only way to overcome this ambiguity is to sample.

The only way to sample is to drill

The only relevant questions relate to our drill sampling strategy:

Which drilling method, how many samples, what spacing, what materials, what elements, what detection limits?

Can we achieve such a strategy in an efficient and cost competitive way at best practice OHS and environmental standards.

This is the business of the DET CRC

Compromise is necessary!

The ideal:

Representative, reproducible, accurately located, no contamination, broadest suite of analyses at lowest detection limits, textural data, rapid acquisition, rapid analyses, cost effective

SAMPLE QUALITY vs SAMPLE DENSITY

Elements of the Plan A new paradigmfor drilling

Real time quantitative data capture

Decision making tools

All Underpinned by knowledge of the host rocks and mineral system!

• ~1,000m Alberta gas wells with 4.5” casing

• 2-3 hours move in and rig up time• 2 wells/day achieved• $US 8,000 per well for drilling• improved cost, safety, environmental

impact and hole stability in minex

• key challenges for minex include: coil durability, low WOB drilling

• initial target: • greenfields rig to 500m, less than 5

tonnes and $50/m

PROGRAM 1: Drilling Technologies

Coiled Tube drilling for MinEx

AdvantagesCheap and rapid drillingLight, small footprint – access and enviroRapid mobilisationNo drill rods – OHSESample is pulverised and homogeneous

Challenges Accurate location of drill bit (sample)Depth fidelity and contaminationCan it be done?

Program 2: Logging and Sensing

Fe contentPGNAA

Bore Hole Radar

Downhole Sensing

AdvantagesReal time, at site analysesSingle deployment – while you drillMost wireline techniques applicable without significant compromise on data qualityGeophysical logging

Challenges Down hole environment challenging for geochem and mineralogyWhat do you do with all the data?

10x vertical exaggeration

10 km

2 km

N10 km

Emmie Bluff3D ModelAlteration voxet

Emmie Bluff

Sericite

HematiteMagnetiteHematite – Magnetite

K-FeldsparAlbite

Sericite – ChloriteChlorite

500 m x 500 m x 10 m cell size

Program 3 Deep Targeting

Top hole Sensing

AdvantagesReal time, at site analysesSingle deployment – immediately following drillingExisting techniques for geochem and mineralogy (eg. pXRF/XRD and hyperspectral scanners)

Challenges Sample quality depends on drilling and sampling techniques (Program 1)Compromise on detection limits…

Scale of footprint depends on sampling and analytical methodology!

(Image from S. Halley)

Detection limit critical for single element footprint

However for pattern recognition at scales appropriate to exploration multiple streams of lesser quality but higher density data, delivered in real time to inform decision making are extremely useful…

Portable XRF – analyses as quick as you can dril

Can you see the pattern?

• IOCGs, Gawler Craton, SA

• drill through deep cover based on grav & mag anomalies alone

• many false +ves• many anomalies

tested by one hole• sparse data

collected with little knowledge to inform follow-up drilling

Current Practice

Source: Simon van der Wielen

Image courtesy of Simon van der Wielen

Olympic DomainDET CRC Deep

Prospecting Strategy

Identify target based on geophysics and prior

drilling

Subtle feature in regional gravity survey



Systematically sample target area with cheap,

rapid drilling +real time analyses

Hole on gravity high ‘fails’ but pathfinder geochemistry in all

holes hints at a broader pattern and informs

follow up drilling

5km grid pattern

Pathfinder element X

Anomaly

Background

9 holes~400m$50/m

=$180K


Anomaly

Background



Prioritise follow up drilling on-the-fly

Expand drill pattern and chase geochemical

gradients toward the east and north

Identify alteration footprint

5km grid pattern

‘failed’ initialtarget

56 holes=$1,120K


Anomaly

Background



Prioritise infill drilling on-the-fly

Identify hot-spots within the footprint for deep

targeting with high level of confidence

5km grid pattern

‘failed’ initialtarget

89 holes=$1,780K



Expanded regional survey identifies new target zones for infill

and follow-up drilling

Begin to map the mineralising system


Anomaly

Background

Targets based on broad bandwidth of data reduces false

+ves and allows recognition of new

deposit styles

Documents

Deep Exploration Technologies CRC: Uncovering the Future