Partial Extraction Method for Normative Mineralogy

Partial Extraction Method for Normative Mineralogy Estimation at Antucoya Mining CompanyGonzalo Mendoza, Mauricio Garrido, Gonzalo Fuster, Juan Moya, Héctor Montes, Daniele Beck, and Francisco Contreras

Agenda• Introduction

– Project Overview– Deposit Mineralization

• Development– Dissolution of Copper Minerals– Partial Extraction Method– Normative Mineralogy Calculations– Determination of Endmembers’ Solubility– Antucoya Mine’s Endmembers– Antucoya Mine’s Partial Extraction Samples – Available Modal Mineralogy– Alternative Calculation of Normative Mineralogy

• Conclusions

IntroductionProject Overview

W E

Antucoya belongs to the AntofagastaMinerals Group and considers theproduction of ~ 80 kton of fine Cu. Itis located 125 km northeast ofAntofagasta city.

The process considers the extractionand leaching oxidized ores to producecopper cathodes through SX-EWprocess. Its current resources exceed1,000 Mton @ 0.33% Cu.

Mineralization associated with Cretaceousporphyries (140-142 Ma) embedded in Jurassicrocks of the La Negra Formation. Thedevelopment and evolution is associated withAtacama Fault Zone (ZFA).

IntroductionDeposit Mineralization

Antucoya Sector:

• Development in a low acidic environment (pH 4-7), presence ofreactive gangue (Mt, chl, k-fs, etc.) and rocks having little pyrite.

• In situ oxidation of Cu oxides such as atacamite, chrysocolla, copperpitch, brochantite.

• There is no development of secondary enrichment.

Buey Muerto Sector:

• Development in a high acidity environment (pH 2-4), with lesseramount of reactive gangue (Qz-Sericite) and abundant Py.

• Copper / iron sulfate precipitation and clay formation.

DevelopmentDissolution of Copper Minerals

Dissolution of copper minerals

• Studies on the partial extraction of copper from its minerals date backto the 1930s.

• Brown (1931) studied the solubility behavior of oxides, mixed, andhypogene ores using sulfuric acid, acid ferric sulfate, ammonia andammonium salts.

• The differentiated solubility of pure samples (endmembers) is the basisof the Sequential Copper (Parkinson and Bhappu, 1995) and PartialExtraction (Preece et al., 2017) methods.

• Depending on the mineralogical arrangement of the deposit, thechemical results can be transformed into normative mineralogyestimates *.

* Normative mineralogy is the calculation of the idealized composition of a mineral sample from its chemical assays.

DevelopmentPartial Extraction Method

(TCu): Total copper

(SCu): Sulfuric acid soluble copper

(CNCu): Cyanide soluble copper

(FSCu): Ferric soluble copper

Muestreo

Preparación de

muestras

Identificación arreglo

mineralógico

Generación de

endmembers

Extracción Parcial

muestras

Extracción Parcial

endmembers

Análisis de datos

Cálculo mineralogía normativa en base de datos

Estimación mineralogía normativa en modelo de

bloques

• General scheme representing the Partial Extraction assays.

• Workflow for estimating normative mineralogy.

• The method allows mapping the spatial variability of the different chemical assays.

DevelopmentNormative Mineralogy Calculations

Deposit: Porphyry copper, mainly secondary andhypogenic.

Mineralogy: chalcopyrite (Ccp), Chalcocite (Cct), covellite(Cv)

Chalcocite+Covellite

A subset of samples were characterized by TESCAN modal mineralogy.

Comparison of predictive quality of normative versus modal mineralogy.

DevelopmentDetermination of Endmembers’ Solubility

Endmember estimates: Experimentally (Measured) and mathematically (Estimated)

Mathematical method, combining results from modal mineralogy (TESCAN or equivalent) and Partial Extraction

A = (WT*W)-1*WT*Z

Matriz Endmembers

(A)Matriz

resultadosTESCAN

(W)

Matriz resultados

PTXT

(Z)

=*

Experimental method using pure samples testes by Partial Extraction

DevelopmentAntucoya Mine’s Endmembers

Location of endmembers within solubility diagram

FSCu / CuT versus CNSCu / CuT

• 80% of the copper is present as illite + Cu, SO4 + Cu, FeOx + Cu, and szomolnokite + Cu. Only 20% of copper is related to atacamite, malachite, chrysocolla, with minor content of chalcocite, covellite, and chalcopyrite.

• Mineralogical assemblage was determined from TESCAN modal mineralogy.

• Endmembers’ solubility was determined mathematically using Antucoya data and published information.

• Partial Extraction method was supplemented using water soluble copper to account for copper sulfates:

• (TCu): Total copper

• (SCu): Sulfuric acid soluble copper

• (CNCu): Cyanide soluble copper

• (FSCu): Ferric sulfate copper

• (WSCu): Water soluble copper

DevelopmentAntucoya Mine’s Partial Extraction Samples

DOM scu.cut cnscu.cut wscu.cut fscu.cut

PRI: 361 28% 28% 3% 30%

OXN-LIM: 3,579 45% 34% 7% 47%

OXV: 2,241 63% 46% 4% 65%

SULF: 3,415 58% 55% 23% 60%

TOTAL: 9,596 53% 44% 12% 55%

DevelopmentAvailable Modal Mineralogy

• Campaign 2019-DDH: 131 samples with TESCAN and 14 duplicates.

• Campaign 72 MINICOLUMNS: 72 samples with TESCAN and 7 duplicates.

• Campaign 98 DDH PRIORITY 2: 98 samples with TESCAN and 10 duplicates.

Spatial distribution of TESCAN mineralogy samples

DevelopmentAlternative Calculation of Normative Mineralogy

• For each sample, the copper extraction ratios are considered as coordinates (x1, x2, x3, x4) within the solubility diagram.

• The fraction of copper contained in each mineral is calculated based on the distance from the sample to the endmembers (in the solubility diagram).

d1

d2

d4

d5

(x1, x2, x3, x4)

d6

d7d10

d8

d3

d9d11

• The value of "p" is adjusted to specify the degree of

influence of the endmember.


For each Partial Extraction result, the normative mineralogy is calculated.


• The complexity of the copper-bearing assemblage results in a semi-quantitative estimation of mineralogy.

• The (normative) mineralogy of each sample is reported as a fraction of the copper contained in each endmember.

• Database with normative mineralogy is used to populate the geometallurgical block model.


Illite + Cu FeOx + Cu

Main copper-bearing phases of the deposit are Illite + Cu and FeOx + Cu (having good solubility).


Goethite + Cu Chalcopyrite

Correct identification of areas having low solubility ratio, and ore associated with goethite + Cu (very reddish rock)


Copper Sulphates Szomolnokite + Cu

Correct identification of BueyMuerto areas having copper sulfates and Szomolnokite + Cu


Chrysocolle Copper Phosphates

Correct identification of zone having chrysocolla and copper phosphates as pseudo-malachite.

Conclusions● This work presents the new methodology implemented to improve Antucoya Mine’s mineralogy interpretation.

● The general workflow considered:

● Creation of Partial Extraction databases from certificates of chemical assays,

● Quality control of the data integrity,

● Endmember's identification using advanced mineralogy and Partial Extraction results.

● The Partial Extraction solubility ratios were transformed into normative mineralogy estimates using a

mathematical method based on inverse weighting distance estimation.

● Normative mineralogy estimates were interpolated within the geometallurgical block model to verify that this

new mineralogical interpretation was consistent with the geological knowledge of the deposit.

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Partial Extraction Method for Normative Mineralogy