The 2021 technical report provides an interim resource update for the Castelo de Sonhos Gold Project in Pará State, Brazil, incorporating new drilling, a refined geological model, and an improved estimation methodology.
Report context
This technical report, with an effective date of December 31, 2020, and dated April 30, 2021, was prepared for TriStar Gold Inc. to update mineral resource estimates in advance of a planned Pre-Feasibility Study. The update incorporates drilling from 2019-2020 that post-dates the previous resource estimate, a new high-precision LIDAR survey of topography, and a new geological interpretation and digital model developed using machine learning tools. The project is located in south-western Pará State, Brazil, approximately 20 km north-east of the town of Castelo dos Sonhos. The mineral resources reported within a pit shell total 40.1 Mt at 1.2 g/t Au (1.5 Moz) in the Indicated category and 22.2 Mt at 1.0 g/t Au (0.7 Moz) in the Inferred category, using a 0.3 g/t cutoff.
Processing route
Metallurgical testwork overview
Metallurgical test work has confirmed that the significant majority of gold occurs as free grains. Simple gravity methods of recovery achieve high recoveries, above 80% in lab-scale Knelson centrifuges and above 70% in bulk gravity concentration tests performed with material ground to 75 microns.
Comminution characteristics
Abrasion and grinding tests of the Castelo de Sonhos quartzites show that they are abrasive and of medium hardness. Standard Bond comminution testing results are reported in the testwork data.
Cyanidation performance
Cyanidation tests show that high recoveries can be achieved with low reagent consumption, with or without pre-concentration by gravity methods. Tests of a combination of gravity recovery and cyanidation on material ground to 75 microns show that total metallurgical recoveries of 98% can be achieved with Castelo de Sonhos material in the 1-2 g/t range.
Testwork on alternative processing options
Flotation testwork was performed on rougher gravity tailings and on whole run-of-mine material. Results from flotation of rougher gravity tailings and whole ROM flotation are reported in the testwork data. Flotation concentrate cyanidation results are also documented in the original report.
Proposed flowsheet in previous study
The 2018 Preliminary Economic Assessment developed a plan for a conventional carbon-in-pulp process plant that could produce 150,000 oz of gold annually from 3,000,000 tonnes of run-of-mine material with an average grade of 1.5 g/t, assuming a metallurgical recovery factor of 95%.
Proposed design from testwork recommendations
The report recommends that the upcoming Pre-Feasibility Study include a trade-off study of the technical and economic viability of pre-concentration by gravity and flotation and leaching of concentrates, with recovery around 94%, versus whole ROM leaching, CCD and Merrill Crowe recovery.
Key reported parameters
| Parameter | Value | Units | Basis |
|---|---|---|---|
| Indicated resource tonnage | 40.1 | Mt | Design estimate at 0.3 g/t cutoff |
| Indicated resource grade | 1.2 | g/t Au | Design estimate at 0.3 g/t cutoff |
| Indicated metal content | 1.5 | Moz | Design estimate at 0.3 g/t cutoff |
| Inferred resource tonnage | 22.2 | Mt | Design estimate at 0.3 g/t cutoff |
| Inferred resource grade | 1.0 | g/t Au | Design estimate at 0.3 g/t cutoff |
| Inferred metal content | 0.7 | Moz | Design estimate at 0.3 g/t cutoff |
| Metallurgical recovery (gravity + cyanidation) | 98 | % | Testwork, material at 1-2 g/t, ground to 75 microns |
| Gravity recovery (lab-scale Knelson) | >80 | % | Testwork |
| Gravity recovery (bulk concentration) | >70 | % | Testwork, material ground to 75 microns |
| Assumed metallurgical recovery (2018 PEA) | 95 | % | 2018 PEA design |
| Proposed plant throughput (2018 PEA) | 3,000,000 | t/yr | 2018 PEA design |
| Gold price assumption (2018 PEA) | 1,250 | US$/oz | 2018 PEA design |
| Processing + G&A cost (resource cutoff) | 12 | US$/t | Design parameter |
| Gold cutoff grade for resource reporting | 0.3 | g/t | Design |
| Block model dimensions | 20 x 20 x 4 | m | Design |
| Median gold grain size | ~100 | microns | Testwork |
| Average grade range for viable mineralization | 1-2 | g/t | Historical operating data from drilling |
| Maximum open-pit depth (drilling tested) | ~150 | m | Historical operating data |
| 2018 PEA estimated plant OPEX | 9.99 | US$/t processed | 2018 PEA |
| 2018 PEA estimated mining OPEX | 2.17 | US$/t | 2018 PEA (contract mining) |
| 2018 PEA estimated annual G&A cost | 2.0 | US$ million/yr | 2018 PEA |
| 2018 PEA total CAPEX estimate | 184 | US$ million | 2018 PEA |
Project website: https://tristargold.com/project/castelo-de-sonhos-gold-project/
Project website: https://tristargold.com/
Project website: https://tristargold.com/project/technical-report/
Technical qualifications
The QP responsible for resource estimates is not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing or political factors that might materially affect these mineral resource estimates. Mineral reserves have not yet been estimated for the project. The QPs have not independently verified land title and the status of mineral concessions. The QP for the geology and resource sections last visited the project site in September 2019. The QP for the mining, processing and economic assessment sections has not visited the project site. The non-independent QP is a Vice President of TriStar Gold Inc. The resource estimate was prepared in accordance with the CIM Definition Standard and CIM Best Practice Guidelines, using geostatistical methods, plus economic and mining parameters appropriate to the deposit during the next ten years. These are mineral resources and not reserves and as such do not have demonstrated economic viability. All figures have been rounded to show the appropriate precision for the estimates.
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*Source: NI 43-101 Technical Report titled "Mineral Resource Update for the Castelo de Sonhos Gold Project, Pará State, Brazil," effective date December 31, 2020, dated April 30, 2021.*
