THE EFFECT OF GEOLOGICAL STRUCTURES IN THE EXPLORATION FOR PRIME COKING COAL

Transcription

1 THE EFFECT OF GEOLOGICAL STRUCTURES IN THE EXPLORATION FOR PRIME COKING COAL J Sparrow*, N Wagner + and R Falcon + *Coal of Africa Pty Ltd + University of the Witwatersrand, RSA

2 CONTENTS 1. INTRODUCTION 2. BACKGROUND Exploration In SA and region Coking Assessments Results and anomalies 3. METHODOLOGY and RESULTS Petrography Structural geology Predictions 4. CONCLUSIONS

3 INTRODUCTION Carbon in the form of prime or blend coke is the most important element in the reduction of metallic ores in the iron steel and ferroalloy industry particularly so in South and Southern Africa which host the world s largest chrome, platinum, vanadium, manganese, copper and iron ore deposits Due to the shortage, cost and availability of carbon, exploration for coking coals continues urgently and, more specifically, in the northern coal basins of South Africa and nearby regions. In the past 4 years, numerous laboratory tests have indicated that the coals being examined are of excellent prime coking quality. However, despite those results, in certain areas the coals were found to lack the typical strength required for metallurgical cokeswhen tested in pilot and full-scale coking ovens. Extensive research was then undertaken to establish the reasons for these anomalies.

4 CONTENTS 1. INTRODUCTION 2. BACKGROUND Exploration in South Africa and region Coking Assessments Results and anomalies 3. METHODOLOGY and RESULTS Petrography Structural geology Predictions Coking tests 4. CONCLUSIONS

5 Locality Tuli Coalfield and Soutpansberg Coalfield x x COAL FIELDS OF SOUTH AFRICA 5

6 Weathering profile

7 Vele general stratigraphy Main Strat Sub-Seams Strat.col Sample No. Thick (m) Description TU 3.00 Mudstone, with coal/mudstone horizons 2.50 Mudstone, grey with occ coal stringers Top Seam TM T Mudstone, grey with occ coal stringers TL T Coal bands with mudstone parting PART 6.28 Mudstone, grey, rootlets bioturbation Middle Seam M Coal bands with mudstone parting B11 Gritty, white sandstone marker at base of coal 2.45 Mudstone, grey, with slt and grit sst bands and occ coal bands Bottom Seam BU B1-B BM B BL B5-B Dwyka Group Pre-Karoo FLOOR B Brown Mudstone Tilloid Tillite Gneiss, Granite

8 Vele geology (Tuli Coalfield) N S Commentary Average dip < 2º Open cast mining to 70m Strip ratio (ave): 4.2:1 Underground > 70m depth Average Thickness 1.5m 1.2m 2.1m 3.6m 8

9 Vele geological modeling (floor geometry) N Weathering Surface 8 x Vertical exaggeration Bottom Lower Coal seam floor 9

10 GRAPHIC LOCATION OF SAMPLING OF COAL FOR TESTING IN THE VELE COLLIERY, TULI COALFIELD Vele Colliery: first area planned for mining. The initial bulk samples were taken in the grey area KEY: Dotted lines faults Grey block first mined area Pink Nos & dots -boreholes

11 Fault line Sample 1 Sample 3

12 Relationship of the faulting

13 Metallurgical Coal Trends Decreasing Phos Increasing CSR Increasing Rank Increasing Yield 13

14 RESULTS OF LABORATORY SCALE ANALYSES AND TESTS FROM VELE COALFIELD -1 GROUPED ANALYSES ANALYSIS ad VELE SAMPLE 1 IDEAL VALUES Proximate Inh. Moisture% 1,1 <3 Ash% 10,0 <10 Volatiles% 35, Fixed C% 53,1 >50 Total S% 1,15 <1,5 Calorific Value MJ/kg 30,97 - Coking tests Swelling Index Roga Index 85,0 >45 Plasticity Maximum Fluidity Temp ddpm Dilatation Maximum Contraction % Maximum dilatation %

15 RESULTS OF COKE OVEN TESTS FROM VELE COALFIELD COMPARED AGAINST LOCAL & INTERNATIONAL NORMS -2 GROUPED ANALYSES ANALYSES VELE SAMPLE 1 IDEAL VALUES PLASTICITY Temp Maximum Fluidity T o C Maximum Fluidity ddpm T o C Plastic range T o C DILATATION Softening Temp o C HOT STRENGTH Temp of maximum contraction o C Temp of maximum dilatation o C Maximum contraction % 28, Maximum dilatation % 46, COKE OVEN TESTS Coke Hot Strength after reaction % (CSR) 16,3 >30 (30-73) MICUM Micum >40 (M40) 41,9 >88 (75-90) IRSID Irsid >40 (I40) 14,8 >49 UNACCEPTABLE CSR AND M40/I40 RESULTS

16 RESULTS OF LABORATORY SCALE ANALYSES AND TESTS FROM VELE COALFIELD SECOND SAMPLE - 3 GROUPED ANALYSES ANALYSIS ad VELE SAMPLE 1 VELE SAMPLE 2 IDEAL VALUES Proximate Inh. Moisture% 1,1 1,9 <3 Ash% 10,0 10,3 <10 Volatiles% 35,9 35, Fixed C% 53,1 52,0 >50 Total S% 1,15 1,06 <1,5 Calorific Value MJ/kg 30,97 30,30 - Coking tests Swelling Index Plasticity Roga Index 85,0 86,8 >45 Maximum Fluidity Temp ddpm Dilatation Maximum Contraction % Maximum dilatation %

17 RESULTS OF COKE OVEN TESTS FROM VELE COALFIELD COMPARED AGAINST LOCAL & INTERNATIONAL NORMS -4 GROUPED ANALYSES ANALYSES VELE SAMPLE 1 VELE SAMPLE 2 IDEAL VALUES PLASTICITY Temp Maximum Fluidity T o C Maximum Fluidity ddpm T o C Plastic range T o C DILATATION Softening Temp o C HOT STRENGTH Temp of maximum contraction o C Temp of maximum dilatation o C Maximum contraction % 28,0 23, Maximum dilatation % 46,0 98, COKE OVEN TESTS Coke Hot Strength after reaction % 16,3 28,5 >20 (50-73) MICUM & IRSID Micum >40 41,9 44,8 >88 (75-90) Irsid >40 14,8 15,3 >49

18 PREDICTED COKING VALUES (CSR)* VERSUS ACTUAL* VALUES USING 100 % VELE COAL 45.0 CSR % VELE Second Vele first samples First Vele first samples % Vele (Trial 5) 100 % Vele (Trial 5) 100 % Vele (Trial 4) 100 % Vele (Trial 3) 100 % Vele (Trial 3) 100 % Vele (Trial 2) 100 % Vele (Trial 1) CSR ACTUAL CSR PREDICT

19 RESULTS OF FIRST COKING COAL TESTS FROM VELE COALFIELD 1. Conventional LABORATORY-SCALE Coking coal analyses showed that the coal samples from Vele Coalfield possessed acceptable values of plasticity and dilatation in ranges typical of Coking Coal from other regions of the world. 2. PREDICTIVE MODELS based upon key parameters indicated that the coals would possess good hot strength and cold strength values (30-40%). 3. However, the PILOT OVEN COKING TESTS for the first sample were shown to have VERY LOW HOT STRENGTH (CSR) AND LOW COLD STRENGTHS (M40) and the second sample only slightly better. Thus, both laboratory-scale analyses and predictive models failed to indicate the possibility of poor pilot scale coking tests in the first batch of Vele coals Further investigations were urgently required..

20 CONTENTS 1. INTRODUCTION 2. BACKGROUND Exploration In SA and region Coking Assessments Results and anomalies 3. METHODOLOGY and RESULTS Petrography Structural geology Predictions 4. CONCLUSIONS

21 PETROGRAPHY VITRINITE SHOWING TYPICAL PSEUDOVITRINITE WITH MICRON-SIZED RANDOM AND PARALLEL DESSICATION CRACKS.

22 PETROGRAPHY VELE COAL SHOWING UNUSUAL FRIABLE NATURE (below) NORMAL VITRINITE

23 RESULTS OF FIRST AND SECOND PETROGRAPHIC ANALYSES FROM VELE COALFIELD - 2 GROUPED ANALYSES ANALYSIS % VELE SAMPLE 1 VELE SAMPLE 2 MACERALS Vitrinite 87,6 86,7 Liptinite 2,6 2,6 Reactive semifusinites 0,7 0,7 Inert Inertinites 3,4 4,3 Mineral Matter 5,7 5,7 TOTAL REACTIVES 90,9 90,0 RANK VITRINITE REFLECTANCE RoV maximum % RoV random % 0,84 0,68 0,84 0,72 ABNORMAL TOTAL Cracks ACT Labs; Wagner, Hans Erasmus 2013 Pseudovitrinite 9 4

24 PETROGRAPHY 2 SI 9 SI 7-8 SI 5 2-D DIAGRAM INDICATING THE PROPORTION OF ABNORMAL MATERIAL IN COAL SAMPLES q The 2 Vele coal samples and 1 Makhado coal (seen separately) represent increasing levels of abnormality in parallel with decreasing swelling indices q The block of Vele samples grouped together in the green box all possessed high swelling indices and were from locations far removed from the site of Samples 1 and 2

25 PETROGRAPHY 2 SI 9 SI 7-8 SI 5 2-D DIAGRAM INDICATING THE PROPORTION OF ABNORMAL MATERIAL IN COAL SAMPLES q The 2 Vele coal samples and 1 Makhado coal (seen separately) represent increasing levels of abnormality in parallel with decreasing swelling indices q The block of Vele samples grouped together in the green box all possessed high swelling indices and were from locations far removed from the site of Samples 1 and 2

26

27 STRUCTURAL GEOLOGY MAJOR STRUCTURAL FEATURES AFFECTING KAROO DEPOSITION IN SOUTHERN AFRICA IN PALAEOZOIC TIMES SUB-CONTINENT WITH GRANITIC ISLANDS (CRATONS) WITH INTERVENING CRUSTAL FRACTURES AND MOBILE BELTS 27

28 STRUCTURAL GEOLOGY MAJOR STRUCTURAL FEATURES AFFECTING KAROO DEPOSITION IN SOUTHERN AFRICA IN PALAEOZOIC TIMES SUB-CONTINENT WITH GRANITIC ISLANDS (CRATONS) WITH INTERVENING CRUSTAL FRACTURES AND MOBILE BELTS VELE AND LIMPOPO BELT COALFIELDS 28

29 STRUCTURAL GEOLOGY. CROSS-SECTIONS THROUGH THE COAL-BEARING BASINS AND THE KAAPVAAL CRATON IN SOUTH AFRICA DURING PERMIAN ZIMBABWE CRATON B Deposition occurred with concurrent movement on the pre-existing fault planes A TULI AND NORTHERN BASINS ON THE LIMPOPO MOBILE BELT PERMIAN PERMIAN KAROO SEA Coal forming environments occurring in Paralic and Limnic environments 29

30 CROSS-SECTIONS THROUGH THE COAL-BEARING BASINS AND THE KAAPVAAL CRATON IN SOUTH AFRICA DURING PERMIAN AND TRIASSIC TIMES ZIMBABWE CRATON B Extensive movement on the pre-existing fault planes occurred during the early breakup of Gondwanaland A TULI AND NORTHERN BASINS ON THE LIMPOPO MOBILE BELT TRIASSIC TRIASSIC PERMIAN PERMIAN PERMIAN 30

31 STRUCTURAL GEOLOGY. GRAPHIC LOCATION OF SAMPLING OF COAL FOR TESTING VELE SAMPLE 1 Ash 10,0% SI -5 CSR 16,3 Abnormal 58% VELE SAMPLE 2 Ash 10,3% SI 8 CSR 28.5 Abnormal 20% MAJOR FAULT KEY: Dotted lines faults Grey block mined area Pink dots -boreholes White circle Vele Sample 1 Red circle Vele Sample 2

32 SUMMARY OF RESULTS On comparing the coal samples that had poor coking qualities in the pilot scale oven, there appears to be a direct correlation between The coals exhibiting poor coke strength (CSR and M40) and The coals with desiccation cracks (pseudovitrinite), fissures and brittle qualities. This in turn appears to relate to proximity to faults in the geological structure of the coalfield Conventional analyses and coking tests did not indicate these abnormal conditions in the coal, nor did they reflect the poor pilot-scale coke oven results. 32

33 CONTENTS 1. INTRODUCTION 2. BACKGROUND Exploration In SA and region Coking Assessments Results and anomalies 3. METHODOLOGY and RESULTS Petrography Structural geology Predictions Coking tests 4. CONCLUSIONS

34 Coking Indicators and Price Limpopo \ Soutpansberg 34

35 Coking Indicators and Price Price FOB Limpopo \ Soutpansberg 35

36 BASED ON COKE MARKETING NOMENCLATURE, NORMAL VELE COAL IS CLASSIFIED AS A SOFT COKING COAL AS INDICATED BELOW Vele Other Limpopo coals: Jutland \Chapudi \Makhado Wildebeestehoek \Generaal \Mount Stuart OTHER LIMPOPO COALS ARE CLASSIFIED AS HARD COKING COALS ON THIS CONVENTIONAL CLASSIFICATION WHEN NOT NEAR FAULTS

37 Conclusions Thus, given that : extensive exploration for coking coals is currently underway in many areas in Southern Africa (northern Limpopo Coalfields and in Mozambique) and that many coalfields are characterised by similar extensively faulted geological features and that conventional chemical and laboratory scale coking tests are insufficient to identify such structures.. It is strongly recommended that, in addition to standard coking coal analyses and tests, v v Detailed petrographic analyses are undertaken in order to fully understand the potential performance of the coal in coking conditions, and that The full geological history and structure of the coalfield are determined.before MAJOR DECISIONS WITH REGARD TO MINE DEVELOPMENT FOR THE PRODUCTION OF COKING COAL ARE MADE. 37

38 THANK YOU