application of core logging data to generate a 3d...

May 8th, 2017 Aristotle University of Thessaloniki - Research Dissemination Centre

Engineering Geology and Innovation: Research –Infrastructure - Sustainable Development

(I.A.E.G)

Application of Core Logging Data to

generate a 3D Geotechnical Block Model

Eleftheria Vagkli, M.Sc.| Senior Geologist,

Skouries Geological-Geotechnical Dpt.

Hellas Gold SA |Eldorado Gold Corp.

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May 8th, 2017

INDEX

Scope, Data collection, Data analysis for the Generation of 3D GeotechnicalBlock model

Skouries Geological and Mining Context (Underground)

Rock Mass Properties - Data Collection

2013-2014 Geotechnical Drilling Program

Detailed Geotechnical logging parameters (Laubscher’s RMR90 components)

RQD - Methodology, Data analysis and Results

Laboratory Results – UCS statistical analysis

Structural Data and Model

Spatial variability assessment of rock mass characterization

GEOTECHNICAL BLOCK MODEL

− Generation and Methodology

− Comparison of high and low confidence Data

− Spatial continuity assessment

RMR Block Model Criteria

ResultsAristotle University of Thessaloniki -

Research Dissemination Centre2

May 8th, 2017

Rock Mass Properties - Data Collection.

• Diamond Core Drilling

• Information from Underground Mapping − GSI – Geological Strength Index –Marinos and Hoek, 2000− Q – Rock Tunnel Quality Index – Barton, 1974− RMR – Rock Mass Rating – Bieniawski, 1989 and Laubscher, 1990

• Laboratory Testing – In-situ Strength− UCS, Young’s Modulus, Poisson’s ratio− Shear Strength− Tri-axial Strength− Point Load (field testing)

Geotechnical Data Analysis

• Software− Dips (local)− Leapfrog (local and external)− Slide and Phase2 (external)− Proprietary external software for spatial continuity assessment

• Consultants− SRK – Vancouver – for underground geotechnical block model− David Rhyss – Structural Geologist− SRK - Cardiff – for open pit design recommendations− Golder Associates – UK & Enveco for hydrogeology

The scope of the Underground block model was to generate a tool to spatially assist with excavationdesign of Skouries Underground Mine.

Generation of 3D Geotechnical Block model

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Skouries Geological Context (Underground)

The Skouries Au-Cu porphyry system occurs within poly-deformed amphibolite grade schist and gneiss of the Vertiskos Assemblage where it is intruded by a pipe-like composite intrusive body of early Miocene age.

• Two prominent lithologies− Porphyry (intrusive)− Schist (biotitic and amphibolitic)

Minor Gneiss

• Three alteration styles− Potassic (shell shape around porphyry)− Propylitic /chloritic (schist mainly)− Argillic (local, structural associated)

• Major structures− Damage zone isolated; lack obvious continuity− Historically recorded as more prominent in schist

• Hydrothermal veining and microdefects prevalent− Impact rock strength ( porphyry and schist)− Heavy veining associated with high grade ore− Zoning not explicitly defined

• Clay degradation− Strength reduction upon exposure− Important geotechnical aspect− Zoning unclear 4

May 8th, 2017

Skouries Mining Context (Underground)

• Sub-level Open Stopping (SLOS) mine beneath planned Open pit

• Underground mine vertical extents from 390mRL to -100mRL

• Crown pillar

Lower

Stopes

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May 8th, 2017

Available geotechnical data

per drilling campaign

Database compilation

(Final Database)

Rock Mass Properties - Data Collection

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• Ten (10) Open Pit Geotechnical drill holes

• Ten (10) SLOS drill holes

• Six (6) infrastructure holes

• All bore holes oriented with triple tube (HQ3)

• In total almost 12,400 m were drilled

2013-2014 Geotechnical Drilling Program N

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May 8th, 2017

Detailed Geotechnical logging _ Recorded parameters

• Total Core Recovery (TCR)

• Rock Quality Designation (RQD)

• Intact Rock Strength (IRS)

• Fracture counts (joints, cemented joints, foliation and mechanical breaks)

• Assessment of joint conditions (roughness, alteration of wall rock, fill type)

• Number of joint sets

• Assessment of micro defects

• Strength of fill in closed features

• Joint Orientation (alpha and beta angle)

LAUBSCHER’ S RMR90 COMPONENTS

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May 8th, 2017

SLOS4_RQD

•Total length of core pieces that are longer than 10cm.

•Consider mechanical and man handling breaks as solid core.

•Consider joints along the core axis as solid core.

ROCK QUALITY DESIGNATION (RQD) - METHODOLOGY

SLOS2_ High RQD:100%

SLOS6_ Low RQD: 20 - 25 % 9

May 8th, 2017

RQD –All Data analysis – Porphyry vs Schist

• UCS data reviewed below +420RL

• All schist grouped together based preliminary analysis (k-altered schist included)

• Review of SLOS-series, UCS data suggests that porphyry has higher strength than schist

• Porphyry UCS mean: 110MPa (StDev=29)

• Schist UCS mean: 90MPa (StDev=29)

Laboratory Results – UCS analysis

• All Data (below +420RL ) suggest that porphyry is more massive than schist

• Potassic altered schist not segregated

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May 8th, 2017

STRUCTURAL DATA

Oriented core data set was considered as highestconfidence data

Lower hemisphere Stereonet of the oriented faults measured inthe drill holes, decline and face mapping.(A) Faults in the porphyry. (B) Faults in the Schist

Joint analysis –Selected Joint Sets in Porphyry and Schist (Underground)

FAULTS

JOINT SETS FOLIATIONDominant fabric (foliation) at NE dip direction (for S1) and SE (for S2)

N

PORPHYRY JOINT SETSSCHIST JOINT SETS

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Porphyry and Schist has different fault trends:

• Porphyry: N-S

• Schist: NW-SE (S1)

May 8th, 2017

Looking West

Plan View

N

FINDINGS

• A total of 39 faults have been modelled.

• The 3D analysis of the structural data indicated limited faults continuity

• No indications of regional intense major fault zones, rather discrete gouge filled structures.

Data Sources:

• Oriented core data (fault andfoliation)

• Drillhole RQD, FF and structuralinterval logging

• In-pit structural mapping (Rhys,others)

• Surface mapping data

• DXFs, scanned sections and plans(fault and foliation)

STRUCTURAL MODEL

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• No significant variance in RQD and PointLoad Test (PLT) data among the upper,middle and lower stopes

• UCS and higher confidence RMR data notnumerous enough to do more advancedper stope assessment

• Variance exists between schist andporphyry for RQD and UCS

• Despite some variance, k-altered schistand schist don’t require segregation forstope and development design purposes

• Recommended to group all stopes(upper, middle and lower), focus onlithology review and isolation of weakerzones

Middle Stopes

Upper Stopes

Lower Stopes

Rock mass characterization - Variability assessment for upper, middle and lower stopes

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May 8th, 2017


The scope of the Underground block model was to generate a tool to spatially assist with excavation

design.

The following workflow has been applied for the generation of the geotechnical block model:

• RQD data was utilized from historical and new (2012 to 2014) drilling data sets

• RQD block model interpolated based on statistically supported criteria.

• RMR90 calculated for a large number of drill holes according to:

RQD data converted to Fracture Frequency rating (0-40 range) using established empirical formulamodified (Priest & Hudson, 1981)

Intact rock strength (IRS) from laboratory testing

Joint condition values determined from new drilling data and SRK’s site logging

All blocks from RMR model populated using FF+IRS+JC= RMR90

For the Final RQD Block Model interpolation thefollowing methodology was used:

• RQD data was adjusted using completed regressionanalysis

• All RQD data was split into 5m intervals

• A two pass ID2 interpolation was completed:

− Small 30x20x10mH porphyry search ellipsoid,30x10x20mH schist search ellipsoid, using only highconfidence data.

− Large 60x40x20mH porphyry search ellipsoid,60x20x40mH schist search ellipsoid, using high andlow confidence data.

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Comparison of high and low confidence RQD DataMethod 1• Nearest Neighbor-blocks estimated from one compositeMethod 2• RQD estimated by Inverse Distance (ID2) from different data types within 20m sphere• Estimated blocks averaged within large 40x40x40 m panels

Spatial continuity assessment for search ellipsoid - Porphyry

Spatial continuity assessment (Average distance between drill holes: 20-50m)

The following search ellipsoids have been applied in order to avoid over-smoothing of the estimated RQD values:

Spatial continuity assessment for search ellipsoid –Schist

Looking North-East Looking North- West

Best spatial continuity dip/dip direction: 60/260

Best spatial continuity dip/dip direction: 65/335

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May 8th, 2017

GEOTECHNICAL BLOCK MODEL- RMR Block Model Criteria

The following approach was used in the RMR90 generation process

• Intact Rock Strength (IRS) recommendations:

− Used representative IRS values for Schist, Potassic Schist and Porphyry

− Applied 25% reduction in IRS rating where RQD<50%

• Fracture Frequency (FF) recommendations:

− Converted RQD to FF based on the empirical relationship derived by Priest and Hudson

− Converted to FF rating presented in Laubscher’s RMR90criteria, assuming three point sets.

• Joint Conditions (Jc):

− Used deterministic values for Jr and Ja for Schist, Potassic Schist and Porphyry lithotypes

− Assumed dry conditions

− Converted Jr and Ja values to corresponding joint roughness, joint alteration and joint infill values using Laubscher’s RMR90 criteria

− Used 25% reduction in fill quality where RQD<50%

− Assumed moderate conditions for large scale joint roughness. Assume curved large scale joint expression with a value of 0.85

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May 8th, 2017

RMR90Model–DrillHoleComparison:4480N

RQDRMR90

High confidence drill hole SLOS 4

RMR90 block data correlates

reasonably well with new high

confidence (SLOS) drill hole logging 17

May 8th, 2017 Aristotle University of Thessaloniki - Research Dissemination Centre

Thank you

Application of Core Logging Data to

generate a 3D Geotechnical Block Model

Eleftheria Vagkli, M.Sc.| Senior Geologist,

Skouries Geological-Geotechnical Dpt.

Hellas Gold SA |Eldorado Gold Corp. 18

May 8th, 2017 Aristotle University of Thessaloniki - Research Dissemination Centre19

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