This prefeasibility-level technical report for the Segovia Project presents mineral resource and reserve estimates, process plant operating data, and metallurgical testwork for the Carla orebody.
Report context
This NI 43-101 Technical Report was prepared by SRK Consulting (U.S.), Inc. for Gran Colombia Gold Corp. on the Segovia Project, which comprises the Providencia, El Silencio, and Sandra K mines, and the Carla Project. The effective date of the report is December 31, 2019. The report provides Mineral Resource and Mineral Reserve estimates prepared in accordance with CIM Definition Standards (2014). Mineral Resources are reported inclusive of Mineral Reserves. The quality of information, conclusions, and estimates contained herein are consistent with the level of effort involved in SRK’s services, based on information available at the time of preparation, data supplied by outside sources, and the assumptions, conditions, and qualifications set forth in this report.
Processing route
Maria Dama process plant flowsheet
GCG ore is processed through the Maria Dama process plant utilizing a process flowsheet that includes crushing, grinding, gravity concentration, gold flotation, concentrate regrinding, concentrate cyanidation, Merrill-Crowe zinc precipitation and refining of both the zinc precipitate and gravity concentrate to produce a final gold/silver doré product. The Maria Dama plant has a capacity of 1,500 t/d.
Historical plant performance
Plant production for the period 2017 to 2019 increased from 293,395 t of ore at an average gold grade of 16.85 g/t Au in 2017 to 451,450 t at an average gold grade of 15.48 g/t Au during 2019. Overall gold recovery has ranged from 93.8 to 95.9% over the period 2017 to 2019. During the period 2017 to 2019 gold production increased from 149,037 to 214,036 ounces. Silver recovery is not monitored but is a relatively minor contributor to overall Project economics. Process plant cash operating costs decreased from US$29.51/t ore processed in 2017 to US$24.42/t in 2019.
Testwork on Carla ore
GCG is planning to mine and process ore from the Carla vein and has conducted metallurgical testwork at SGS Canada on a single test composite that was formulated from selected drill holes and intervals from the Carla vein. The metallurgical program included rougher flotation followed by cyanidation of the reground rougher concentrate using process conditions currently practiced at GCG’s Maria Dama process plant. In addition, whole-ore cyanidation and Bond ball mill work index tests were conducted. The results of this testwork demonstrated that the gold contained in ore from the Carla vein is highly recoverable using the process conditions currently in use at the Maria Dama process plant. Gold and silver recoveries were reported at about 95% and 77%, respectively. SRK has reduced the reported laboratory recoveries by 2% in order to account for inherent plant inefficiencies. As such, overall gold and silver recoveries from Carla ore are projected at 93% and 75%, respectively.
Tailings management
The El Chocho tailings storage facility has been designed as a dry stack TSF. The tailings production rate is currently around 1,500 t/d and may ultimately be increased to 1,600 t/d with a total estimated volume of current tailings storage at 1.28 Mt and future storage of 2.3 Mt to meet the life-of-mine requirements. The current operation features a filter plant with a single plate and frame filter press and three dehydration cells capable of treating the full tailings load of 1,500 t/d of dry solids. There is an emergency pond adjacent to the filter plant for temporary slurry tailings storage when the filter press is down for maintenance. A second filter press is planned for construction in 2021 with the goal of eliminating down time for maintenance and reaching a filtering rate of 1,600 t/d.
The current storage facility consists of existing Phases 1B and 1A and new Phase 1C, which finished construction in February 2020. There is a future Phase 2A planned for construction downstream of Phase 1C. Phase 1B was the first tailings storage facility built and was designed to accept slurry tailings. Phase 1A was designed as interim containment measure while Phase 1C was being constructed. Phase 1C and future Phase 2A were designed by Wood. Filtered tailings are transported from the filter press by haul trucks and spread with a track dozer and compacted with vibratory smooth drum compactor to a specified lift thickness and minimum relative density. The outer 40 m of each tailings lift is compacted to a higher relative density to improve mass and erosional stability of the placed tailings.
Flotation tailings from the Maria Dama process plant are pumped directly to the TSF for filtration and dry stacking. A smaller secondary stream of cyanide tailings is first detoxified using H2O2 and FeSO4, then pumped to one of several settling/holding ponds for temporary storage. The detoxified and dewatered tailings from the four settling ponds will eventually be treated through a polymetallic plant (cleaning plant) to remove lead and zinc before being transferred to the El Chocho TSF. The cleaning plant is currently under construction and should be operational by the end of 2020.
Key reported parameters
| Parameter | Value | Units | Basis |
|---|---|---|---|
| Plant capacity | 1,500 | t/d | Design |
| Plant throughput (2019) | 451,450 | t | Actual |
| Overall gold recovery (2017-2019) | 93.8 – 95.9 | % | Actual |
| Gold recovery – Carla ore (testwork) | 95 | % | Testwork (reported lab) |
| Gold recovery – Carla ore (projected) | 93 | % | Testwork (reduced for plant inefficiencies) |
| Silver recovery – Carla ore (testwork) | 77 | % | Testwork (reported lab) |
| Silver recovery – Carla ore (projected) | 75 | % | Testwork (reduced for plant inefficiencies) |
| Gold recovery assumed for Mineral Resources | 90.5 | % | Assumption based on plant performance |
| Plant feed gold grade (2017) | 16.85 | g/t | Actual |
| Plant feed gold grade (2019) | 15.48 | g/t | Actual |
| Gold production (2017) | 149,037 | oz | Actual |
| Gold production (2019) | 214,036 | oz | Actual |
| Process plant cash cost (2017) | 29.51 | US$/t | Actual |
| Process plant cash cost (2019) | 24.42 | US$/t | Actual |
| Tailings production rate | 1,500 | t/d | Design |
| Future tailings rate (planned) | 1,600 | t/d | Design |
| Current tailings storage volume | 1.28 | Mt | Actual |
| Future tailings storage volume | 2.3 | Mt | Design |
Project website: https://www.scribd.com/document/721346409/GCM-Segovia-PFS-Update-NI43-101-Dated-20220506-Final
Technical qualifications
The report was prepared as a prefeasibility-level study. SRK reviewed all geotechnical data acquired by Geomecanica del Peru Consulting and determined that data from the field geotechnical investigation is appropriate for supporting a PFS based on field observations and the work conducted by GCG. The data collection process is adequate and consistent with international standards for a PFS. More data will need to be incorporated into the PFS geotechnical model to move forward to a feasibility study.
SRK has not updated the Mineral Resource models for the Carla and Las Verticales areas as no new information is currently available and therefore the last estimate remains valid.
A requirement for long-term post-closure water treatment would add significant cost to closure estimates. Detailed geochemical characterization is needed to more accurately understand the potential for mining wastes to generate poor quality contact water that might persist into closure and post closure.
The Mineral Reserve estimates are based on a mine design, mine plan, and economic model. The cut-off grade calculation assumes a $1,350/oz Au price, 90.5% metallurgical recovery, $6/oz smelting and refining charges, $25/t G&A, $26/t processing cost, and mining costs ranging from $76 to $115/t. Costs and prices used for cut-off grade calculation may be somewhat different than those in the final economic model due to the need to make assumptions early on for mine planning prior to finalizing other items and using long term forecasts for the life of mine plan.
Source: NI 43-101 Technical Report – Segovia Prefeasibility Study, SRK Consulting (U.S.), Inc., March 2020, Sections 1.4, 1.5, 1.6, 1.8, 1.9, 1.10, 1.11, 2, 16.
