Deep Exploration Technologies CRC: Uncovering the Future
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Transcript of 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
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
Semi-regular sampling at 40km intervals granite
basalt
limestone
shale siltstone
sandstone
400km
200km
Semi-regular sampling at 20km intervals granite
basalt
limestone
shale siltstone
sandstone
400km
200km
Semi-regular sampling at 10km intervals granite
basalt
limestone
shale siltstone
sandstone
400km
200km
Semi-regular sampling at 5km intervals granite
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
Olympic DomainDET CRC Deep
Prospecting Strategy
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
Pathfinder element X
Anomaly
Background
Olympic DomainDET CRC Deep
Prospecting Strategy
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
Pathfinder element X
Anomaly
Background
Olympic DomainDET CRC Deep
Prospecting Strategy
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
Olympic DomainDET CRC Deep
Prospecting Strategy
Expanded regional survey identifies new target zones for infill
and follow-up drilling
Begin to map the mineralising system
Pathfinder element X
Anomaly
Background
Targets based on broad bandwidth of data reduces false
+ves and allows recognition of new
deposit styles