Sampling data validation using twin holes in a niobium mine · evaluation of mineral deposits, the...

Theory of Sampling and Geostatistics for twin drill holes analysis in a niobium mine in Araxá, Brazil

M T G C M A R Q U E S , T M E L H A J J , J M B R A G A J R , A C C H I E R E G AT I A N D H D E L B O N I J R

Day 1 - Tuesday 9 May 2017

Session 4: Drill and Blast Hole Sampling - 4.40pm -

5.00pm

Presenter: Thammiris M. El Hajj – Professor in the Mining Department of the Federal University of Alfenas in Brazil.

WCSB8 8TH WORLD CONFERENCE ON SAMPLING AND BLENDING 2

Maria T. G. C. Marques Thammiris M. El Hajj José Marques B. Jr.

Ana Carolina Chieregati Homero Delboni Jr.

INTRODUCTION


• Main niobium producer (85% of the world consumption).

http://www.google.com.br/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiD0aWb_fHSAhVGjpAKHd4OBzsQjRwIBw&url=http://g1.globo.com/economia/negocios/noticia/2013/04/monopolio-brasileiro-do-niobio-gera-cobica-mundial-controversia-e-mitos.html&bvm=bv.150729734,d.Y2I&psig=AFQjCNHTmsZ_egs_70vZZtHMFBr0cfzDhw&ust=1490542371962282

http://www.google.com.br/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj9s9nv_fHSAhXCl5AKHZXZBbsQjRwIBw&url=http://www.paautomation.com.br/CBMM-project.php&bvm=bv.150729734,d.Y2I&psig=AFQjCNGKL60lF8rIim6hwVoTqTg36J0BVg&ust=1490542551628498

http://www.google.com.br/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjos7Si_vHSAhXBFJAKHUmBAVYQjRwIBw&url=http://mag.volvotrucks.com/pt-BR/brazil/?art=3929&bvm=bv.150729734,d.Y2I&psig=AFQjCNFB72ks__z9UwQSre2Qc1452gxGNQ&ust=1490542657453224



Brazil 94%

Canada 5%

Other 1% Niobium production (t)

Reserves (t)

2014 2012 2013 2014 (%)

Brazil 10.827.843,00 82.214,00 76.899,00 88.771,00 93,67

Canada 200.000,00 4.710,00 5.260,00 5.000,00 5,28

Other countries nd 375,00 1.000,00 1.000,00 1,05

TOTAL 11.027.843,00 87.299,00 83.159,00 94.771,00 100,00

Production (t)Country

Niobium Ore Discovery Djalma Guimarães.

Carbonatite Complex in Araxá.

CBMM Alphanumeric campaign.

Twin Drill Holes campaign.

FIG 1 – Djalma Guimarães.

Available at: Federal University of Minas Gerais Journal, 2007 ed.

INTRODUCTION


Niobium Ore Discovery Djalma Guimarães.

Carbonatite Complex in Araxá.

CBMM Alphanumeric

campaign.

Twin Drill Holes campaign.

INTRODUCTION


FIG 2 – CBMM and CODEMIG Mine Rights. Available at: Google Earth, 2016 - SIGMINE.

INTRODUCTION

The importance of sampling procedures aligned with reserves estimation.

“The importance of sampling is emphasised especially while considering the evaluation of mineral deposits, the process control and the product marketing. It should be noted that poor sampling can result in sizeable losses or distortions of results with unpredictable technical and financial consequences. Sampling is one of the most complex operations and it can easily introduce errors in the metallurgical and mining industries.”

(Luz et al., 2004)


Original Content (%)

X Y Z W

Sample Content (%)

X Y Z W

Sampling

INTRODUCTION


OBJECTIVE

The objective of this work was to asses whether the data from the 70s campaign is suitable to be used in the pit modeling.

Lithology.

Grade.

Nugget effect.


OVERVIEW

Why apply QA/QC procedures during a twin drill hole campaign

validation?

QA (quality assurance)

Planning: comprises all the measures that need to be planned and materials that need to be

previously acquired;

QC (quality control)

Implementation: consists of all verification procedures required during and after the drilling

program.


OVERVIEW Representativeness “The representativeness must be maintained at all stages of the sampling procedure. By ensuring the precision and accuracy of the samples taken at all stages of the mining chain, the results will be auditable and reproducible.”

(Gy, 1998)


OVERVIEW Twin Drill Holes Technique

“Commonly, the twin holes drilling technique is applied for verification of grades provided by previous drilling. It is important to use it when the reliability of previous campaigns data is questionable, especially when data are collected without rigorously applying the relevant QA/QC procedure.”

(Abzalov, 2009)


F FG

Parameters:

1. Same slope and azimuth;

2. Distance between collar holes less than 5 metres.

Drill Hole Campaigns

OVERVIEW Geostatistics

“When sampling involves two directions (x, y), the most suitable instrument to estimate the dependence between samples is the variogram. The variogram is a basic tool to support the kriging techniques, which allows representing the variation of a regionalised phenomenon in space.”

(Huijbregts, 1975)


sill

Nugget Effect Sample Reproducibility

METHODOLOGY CBMM Geological Model

(“Alphanumeric” Campaign); Twin drill holes location within the

limit of the current pit; Drilling identical samples interval;

Geological domains: soil, orange

weathered ore, brown weathered ore, saprolite and fresh rock.


FIG 4 – Google Earth’s view of the current campaign inside the actual pit and its 11 drill holes chosen to

validate the previous campaign.


Horizontal sections

Vertical sections

3D Geological

Model 490 DDH;

Geological domains: soil, orange weathered ore, brown weathered ore, saprolite and fresh rock.

Software MS3D (Minesight).

METHODOLOGY

Quality Assurance / Quality Control Insertion of control samples;


SAMPLES Duplicate Blank Standard

FREQUENCY 20 35 25

METHODOLOGY


Precision Accuracy

REPRESENTATIVENESS

m²(SE) + σ²(SE) = r²(SE)


DATA BASE

Twin Drill Holes Alphanumeric Holes

Statistical Analysis Statistical Analysis

QA/QC

ASSESMENT

Collar Directory

Assay Directory

Geology Directory

Estimate variance between duplicates

Calculation of the error linked to the sampling

protocol

ASSESMENT METHODOLOGY

+

{


Content Analysis ASSAY

Coordinates Analysis COLLAR

Lithology Analysis GEOLOGY

Horizontal distance between holes

𝑫 = 𝒙𝟏 − 𝒙𝟐 ² + 𝒚𝟏 − 𝒚𝟐 ²

Difference of the elevation between holes (axis z)

+

Statistical analysis of the variable 𝒙𝟏

(𝑵𝒃𝟐𝑶𝟓)

Software SGeMS: Analysis of the grade range variation between pairs

of samples to obtain the nugget effect from semivariogram

0.5*γ(h)

Use the previous value to calculate the standard

deviation σ(h)

Applying stacked column charts to generate drill hole geological profiles

Comparison between the lithological profiles

boundaries

RESULTS AND DISCUSSION


Relative difference between duplicate samples QA/QC

0.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00

Ore

co

nte

nt (%

) -

Dup

lica

te

Ore content (%) - Sample

Quality Control Program DDH Campaign - FG

Lab. SGS - Global

Tendency Line

Sample

Upper Limit 15%

Lower Limit 15%

Refused

Samples

0.00%

ϒ(h)=σ(ℎ)

2

ϒ(h) – estimated semivariogram; σ(ℎ) – standard deviation.

21

Relative standard deviation of the fundamental sampling error during the sample preparation

Stage Mass per lot Sample mass d95 IHL FSE2 FSE (%)

Primary Sample

Selection 30000 15000 3.2 14.65 0.000488477 2.21%

Primary Comminution 15000 15000 0.2 0.01 0 0.00%

Rotary Sampler 15000 2000 0.2 0.01 3.02093E-06 0.17%

Rotary Sampler 2000 250 0.2 0.01 2.43998E-05 0.49%

Pulverization 250 250 0 0.00 0 0.00%

Chemical Analysis 250 50 0 0.00 0.000000128 0.04%

Total 0.00051 2.26%

S² (QFE) = S²(FSE) + S²(GSE) = 2 x s2 (FSE) 0.00103 3.20%

Regarding the fundamental sampling error (FSE) associated to the sampling protocol, a value of 3.20 per cent was obtained and it is in

accordance with the standards adopted by the company. QA/QC



Coordinates Validation COLLAR

Comply with the maximum spacing (horizontally) of 5

metres between the pair of drill holes.

DHID DHID

Horizontal

distance

(cm)

Elevation

difference

(m)

F-0IXM0 FG-0IXM0 1.41 72.4

F-0XM9 FG-0XM9 1.7 43.06

F-0XN0 FG-0XN0 1.26 61.88

F-2IXK5 FG-2IXK5 1.17 50.23

F-2VIIK0 FG-2VIIK0 0.22 2.99

F-3VIIK7 FG-3VIIK7 1.8 27.8

F-5IXK5 FG-5IXK5 2.66 51.1

F-5XIJ3 FG-5XIJ3 1.55 9.42

F-7IXH5 FG-7IXH5 1.35 -2.32

F-8.5VIIL9.5 FG-8.5VIIL9.5 0.99 21.39



Coordinates Validation COLLAR

The twin drill hole FG-7IXH5 was performed on a landfill, and due

to this fact, its height is above the old drill hole

level.

DHID DHID

Horizontal

distance

(cm)

Elevation

difference

(m)

F-0IXM0 FG-0IXM0 1.41 72.4

F-0XM9 FG-0XM9 1.7 43.06

F-0XN0 FG-0XN0 1.26 61.88

F-2IXK5 FG-2IXK5 1.17 50.23

F-2VIIK0 FG-2VIIK0 0.22 2.99

F-3VIIK7 FG-3VIIK7 1.8 27.8

F-5IXK5 FG-5IXK5 2.66 51.1

F-5XIJ3 FG-5XIJ3 1.55 9.42

F-7IXH5 FG-7IXH5 1.35 -2.32

F-8.5VIIL9.5 FG-8.5VIIL9.5 0.99 21.39



Drill Holes Percentage of accepted

samples

F/FG - 0IXM0 samples at different intervals

F/FG - 0NX0 55.4%

F/FG - 0XM9 69.3%

F/FG - 2IXK5 91.7%

F/FG - 2VIIK0 64.4%

F/FG - 3VIIK7 57.1%

F/FG - 5IXK5 75.0%

F/FG - 5XIJ3 58.3%

F/FG - 7IXH5 52.5%

F/FG - 8.5VIIL9.5 samples at different intervals

F/FG - 8VIIK0 57.9%

Content Validation

ASSAY

Variogram applying spherical function

Nugget Effect

0.45 Variance

Standard Deviation

47.4 per cent.

=

{ Upper Limit

Lower Limit




samples

F/FG - 0IXM0 samples at different

intervals

F/FG - 0NX0 55.4%

F/FG - 0XM9 69.3%

F/FG - 2IXK5 91.7%

F/FG - 2VIIK0 64.4%

F/FG - 3VIIK7 57.1%

F/FG - 5IXK5 75.0%

F/FG - 5XIJ3 58.3%

F/FG - 7IXH5 52.5%

F/FG - 8.5VIIL9.5 samples at different

intervals

F/FG - 8VIIK0 57.9%

FIG 5 – Scatterplot of the comparison between F-2IXK5 and FG-2IXK5 drill holes that contain the largest quantity of

samples within the deviation limit of 47.4 per cent.



samples

F/FG - 0IXM0 samples at different

intervals

F/FG - 0NX0 55.4%

F/FG - 0XM9 69.3%

F/FG - 2IXK5 91.7%

F/FG - 2VIIK0 64.4%

F/FG - 3VIIK7 57.1%

F/FG - 5IXK5 75.0%

F/FG - 5XIJ3 58.3%

F/FG - 7IXH5 52.5%

F/FG - 8.5VIIL9.5 samples at different

intervals

F/FG - 8VIIK0 57.9%

FIG 6 – Comparison between the grades of the variable x1 in the drill holes F/FG-2IXK5 and its average. Both holes

have samples at identical intervals; the graph only illustrates the spacing of every 5 m for better visualisation.


FIG 7 – Alphanumeric drill holes that showed better results regarding the conformity with their respective twin drill holes.

Lithology Validation GEOLOGY

Applying stacked column charts to generate drill hole geological

profiles


FIG 8 – Twin drill holes which did not reach a satisfactory depth to be described.



FIG 9 – Twin drill holes with slight discrepancy among its respective original hole, which ranged from 2.5 to 5.0 metres between the lithological contact.



FIG 10 – Pair of drill holes with significant discrepancy between the lithology’s delimitation involving brown wethearing ore, the saprolite and the rock.




As previously reported, the accepted representativeness value is 1.0.

Although, some samples resulted in different values, they are not inadequate when referring the average of 𝑁𝑏2𝑂5 content in both drill holes.


CONCLUSIONS

Effectiveness of the applied methodology.

Distance between the holes regarding the coordinates validation.

High value expected for the nugget effect.

QA/QC procedures benefits.


CONCLUSIONS

The objective of this paper was to provide helpful information regarding the use of a methodology that associates the TOS with Geostatistics to validate old drilling campaigns, along with its economic benefits and practicality.

The new campaign samples, which were obtained following a QC campaign, are suitable to evaluate the old campaign data.


CONCLUSION


Twin Drill Hole Campaign

New Campaign

ACKNOWLEDGEMENTS

The authors kindly thank the support and permission to publish the paper by CBMM. Moreover, the researchers express their

sincere gratitude to the company’s mine planning department, especially the geology team.



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