Application of Core Logging Data to generate a 3D Geotechnical Block Model

Transcription

1 Application of Core Logging Data to generate a 3D Geotechnical Block Model Engineering Geology and Innovation: Research Infrastructure - Sustainable Development (I.A.E.G) Eleftheria Vagkli, M.Sc. Senior Geologist, Skouries Geological-Geotechnical Dpt. Hellas Gold SA Eldorado Gold Corp. Aristotle University of Thessaloniki - Research Dissemination Centre 1

2 INDEX Scope, Data collection, Data analysis for the Generation of 3D Geotechnical Block model Skouries Geological and Mining Context (Underground) Rock Mass Properties - Data Collection 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 Results Aristotle University of Thessaloniki - Research Dissemination Centre 2

3 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 Generation of 3D Geotechnical Block model The scope of the Underground block model was to generate a tool to spatially assist with excavation design of Skouries Underground Mine. 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 3

4 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

5 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 Aristotle University of Thessaloniki - Research Dissemination Centre 5

6 Rock Mass Properties - Data Collection Available geotechnical data per drilling campaign Database compilation (Final Database) 6

7 Geotechnical Drilling Program 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 N Aristotle University of Thessaloniki - Research Dissemination Centre 7

8 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 8

9 ROCK QUALITY DESIGNATION (RQD) - METHODOLOGY 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. SLOS4_RQD SLOS2_ High RQD:100% SLOS6_ Low RQD: % 9

10 RQD All Data analysis Porphyry vs Schist All Data (below +420RL ) suggest that porphyry is more massive than schist Potassic altered schist not segregated Laboratory Results UCS analysis 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) 10

11 STRUCTURAL DATA FAULTS Oriented core data set was considered as highest confidence data Lower hemisphere Stereonet of the oriented faults measured in the drill holes, decline and face mapping. (A) Faults in the porphyry. (B) Faults in the Schist Porphyry and Schist has different fault trends: JOINT SETS Joint analysis Selected Joint Sets in Porphyry and Schist (Underground) Porphyry: N-S Schist: NW-SE (S1) FOLIATION Dominant fabric (foliation) at NE dip direction (for S1) and SE (for S2) N PORPHYRY JOINT SETS SCHIST JOINT SETS 11

12 STRUCTURAL MODEL Looking West Plan View Data Sources: Oriented core data (fault and foliation) Drillhole RQD, FF and structural interval logging In-pit structural mapping (Rhys, others) Surface mapping data DXFs, scanned sections and plans (fault and foliation) 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. 12

13 Rock mass characterization - Variability assessment for upper, middle and lower stopes No significant variance in RQD and Point Load Test (PLT) data among the upper, middle and lower stopes Upper Stopes UCS and higher confidence RMR data not numerous enough to do more advanced per stope assessment Variance exists between schist and porphyry for RQD and UCS Middle Stopes Despite some variance, k-altered schist and schist don t require segregation for stope and development design purposes Lower Stopes Recommended to group all stopes (upper, middle and lower), focus on lithology review and isolation of weaker zones 13

14 GEOTECHNICAL BLOCK MODEL 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 formula modified (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 the following methodology was used: RQD data was adjusted using completed regression analysis All RQD data was split into 5m intervals A two pass ID 2 interpolation was completed: Small 30x20x10mH porphyry search ellipsoid, 30x10x20mH schist search ellipsoid, using only high confidence data. Large 60x40x20mH porphyry search ellipsoid, 60x20x40mH schist search ellipsoid, using high and low confidence data. 14

15 GEOTECHNICAL BLOCK MODEL Comparison of high and low confidence RQD Data Method 1 Nearest Neighbor-blocks estimated from one composite Method 2 RQD estimated by Inverse Distance (ID 2 ) from different data types within 20m sphere Estimated blocks averaged within large 40x40x40 m panels 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 - Porphyry Spatial continuity assessment for search ellipsoid Schist Looking North-East Best spatial continuity dip/dip direction: 60/260 Looking North- West Best spatial continuity dip/dip direction: 15 65/335

16 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

17 RMR90Model DrillHoleComparison:4480N High confidence drill hole SLOS 4 RMR90 RQD RMR90 block data correlates reasonably well with new high confidence (SLOS) drill hole logging 17

18 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. Thank you 18 Aristotle University of Thessaloniki - Research Dissemination Centre

19 Aristotle University of Thessaloniki - Research Dissemination Centre 19

20 Aristotle University of Thessaloniki - Research Dissemination Centre 20

21 Aristotle University of Thessaloniki - Research Dissemination Centre 21

22 Aristotle University of Thessaloniki - Research Dissemination Centre 22