Comprehensive mineralogical characterisation at the Cerro Corona Cu-Au porphyry mine – The fundamental key for geometallurgical applications. R. BAUMGARTNER, P. GOMEZ, G. ESCOBAR
For today… ● Why a mineralogical characterisation? ● Geology of Cerro Corona ● Alteration types ● Quantitative mineralogy and its application for geometallurgy ● Information from textures, grain size and liberation ● Predictions of copper recovery using mineralogy ● Identification of copper and gold losses in plant tails from head samples ● Conclusions
Mineralogical characterization Daily problems in the processing plant ● Why: Demonstrate that mineralogy can be used for operational geometallurgy and provide important information for orebody knowledge and ore behaviour prediction. ̵ Understand the mineralogical differences between the different alteration types (in particular in argillic alteration) ̵ Relate mineralogical textures with mineralisation occurrences. ̵ Identify potential copper and gold losses. ̵ Predict copper recoveries using mineralogical information ● How: Group the geology, mining, geometallurgy, and metallurgy teams for the programme planning so that everybody feels involved (…and will use the information). Well thought multi-purpose sampling campaign. Make sure that the right methods are used. ● What: Detailed quantitative mineralogical study with multiple methods to make sure that the results are valid and robust. Comprehensive interpretation of data.
Regional Geology ● Cerro Corona quartz diorite stock emplaced in a sequence of carbonate rocks and at a loci of fault intersections.
Miocene porphyritic quartz diorite stock
Geology at Cerro Corona Intrusion phases ● The porphyry mineralisation is composed of several magmatic pulses. Four out of six are mineralised. ● Typical Cu-Au porphyry mineralisation overprinted by a late Au-(Cu) epithermal mineralisation.
Structures Faults Veinlets Veins
Intrusion phases
Uzategui et al, 2016
Several magmatic pulses overprinting of alterations
Geology at Cerro Corona Alteration types
Alterations
● Argillic alterations subdivided according to the types and amount of clays ● Silicification consists of stockwork with different vein types.
Uzategui et al, 2016
Sub-facies of argillic alteration
different processing responses
Geology at Cerro Corona Alteration type Alteration
Key minerals
Principal sulphide assemblages
Occurrence
Argillic 1 (ARG1)
Quartz, kaolinite, muscovite (illite), smectite
Fe sulphides-chalcopyrite (± chalcocite+covellite)
Shallow and deeper parts
Argillic 2 (ARG2)
Quartz, feldspars, montmorillonite, kaolinite, illite, carbonates
Chalcopyrite-(Fe-sulphides)
Overprinting locally K, SIL, and ARG 3 alteration
Argillic 3 (ARG3)
Quartz, montmorillonite muscovite (illite), chlorite
Chalcopyrite-(Fe-sulphides), secondary copper minerals
Upper parts of the deposit, generally the product of weathering & supergene alteration
Geology at Cerro Corona Alteration Alteration type
Silicification (SIL)
Potassic (K)
Key minerals
Quartz, Fe oxides
Quartz, K-feldspar, biotite, Fe Oxides (magnetite)
Principal sulphide assemblages
Occurrence
Fe sulphides-chalcopyrite -(bornite)
As intense stockwork around barren cores.
Chalcopyrite-(bornite, Fe-sulphides)
Abundant in deep parts, and core of the quartz-diorite stocks
2 cm
Detailed Mineralogical Study Sample types
● Drill hole samples (DDH, 6m adjacent intervals) ● Pit wall samples (10kg channel sample) ● Production polygons (split of blast holes composite) Alteration
Spatial distribution
Polygons Pit wall
DDH
Total samples
SIL ARG1 ARG3 K ARG2 SSH (Supergene)
9 3 11 4 2 4
11 14 6 0 1 0
6 6 5 11 5 0
26 23 22 15 8 4
Total
33
32
33
98
Methods and testing completed Analyses and testing
● Quantitative mineralogical analysis (Qemscan) ̵ Modal mineralogy ̵ Grain size for Cu and Au minerals ̵ Liberation and associations for Cu and Au minerals ● Semi-quantitative XRD ̵ Clay types ● Rougher laboratory flotation tests ̵ Rougher recovery for Cu and Au ̵ Standard lab conditions than other flotation tests conducted at the mine for comparison.
Mineralogical results Fe sulphides
● Two types of pyrite present at Cerro Corona, along with marcasite ● The amorphous-type pyrite is a recrystallised pyrite and in general related to the late Au-(Cu) epithermal event. ● It contains Au and As in relatively high contents (up to 46 ppm Au and up to 6% As). ● Can be distinguished during Qemscan measurements using the Fe and S contents. ● Different behaviour during flotation. Since the amorphous-type pyrite contains Au, there is a loss of gold in the cleaner circuit, resulting in the decrease in the overall gold recovery.
Two types of pyrite
Mineralogical results Micro-textures – chalcopyrite occurrence
● Micro-textures provide information for processing. ● The spatial distribution of these micro-textures is key for mine planning and processing. ● Alteration type dependent.
Modified from Amstutz, 1961
Simple and complex intergrowths
Mineralogical results Micro-textures
● For some of them, a solution is possible to increase recovery. ● For others, it is likely that the particles containing a mineral of interest will be lost in the tails. ● The solution to increase recovery is not always economic.
Modified from Amstutz, 1961
Impact on processing
Liberation and associations of chalcopyrite By alteration type
Liberated
Liberation
Binary
Ternary / complex
Associations Variable between alteration types
Prediction of copper recovery using mineralogy Chalcopyrite recovery
● Quantitative mineralogy can be used to obtain theoretical grade-recovery curves. ● Example from lab flotation tests compared with prediction from mineralogy
Predictive rather than reactive
Prediction of copper recovery using mineralogy Cu recovery prediction
● In the future, it can be applied to monitor the plant effectiveness using daily mineralogical data.
) % ( e t a r t n e c n o c l a n i f n i e d a r g u C
Predicted recovery trend of daily material Plant performance
Recovery (%)
● This will aid monitoring the plant if any recovery problem is due to operational reasons or the nature of the ore.
Predictive rather than reactive
Identification of copper and gold losses Head samples – chalcopyrite
Background Gold Phases Chalcopyrite Bornite Pyrite Fe-Sulfide Amorphous Tennantite Enargite Goethite Quartz K-Feldspar Plagioclase Muscovite
Aid in justifying recovery issues
Identification of copper and gold losses Head samples – gold
● Associations of gold with chalcopyrite will report to the copper concentrate ● Associations of gold with amorphous-type pyrite or pyrite will report to the cleaner scavenger tails. ● Used to justify low recoveries or to predict low recoveries and inform management and plan accordingly.
Prediction and justification
Conclusions Objective accomplished
● The detailed mineralogical characterisation permit to demonstrate that the obtained information can be used for: ̵ Characterizing the deposit and distinguish differences within sim ilar alterations (variability). ̵ Justify copper and gold losses ̵ Prediction of copper and gold recoveries ● Permit to understand better the variability within a same alteration type. ● Refine the geological model (mainly alteration and mineralisation zone models). ● Make people more happy because they received clear answers in “bad days”.
Thank you for your attention!
