Yauricocha Technical Report PEA

This article summarizes the processing information contained in the February 2022 preliminary economic assessment technical report for the Yauricocha operation.

Report context

The Yauricocha Technical Report PEA, dated February 2022, documents a preliminary economic assessment of the Yauricocha property. The report includes a detailed description of the existing mineral processing facility, which is relevant for understanding the basis for the proposed project design. This article presents the processing-related information from that report.

Processing route

Plant Overview

The Yauricocha operation includes a conventional, multi-stage differential flotation plant with two parallel processing circuits: one for polymetallic mineralized material and one for oxide mineralized material. Each circuit consists of a crushing stage, grinding, sequential differential flotation, dewatering of concentrates, and thickening and disposal of flotation tails.

The original combined capacity of the two circuits is 3,600 tonnes per day. The polymetallic circuit historically operated at a nominal capacity of 3,000 tonnes per day and the oxide circuit at 600 tonnes per day, though ongoing improvements have been increasing daily throughput. No oxide mineralized material has been processed since 2018. Current plant production includes only three mineral concentrates: lead sulfide concentrate, copper sulfide concentrate, and zinc concentrate.

Recent Improvements

Reported recent improvements to the processing facilities include:

• Addition of one OK-50 flotation cell to add capacity to the Cu-Pb bulk flotation stage.
• Installation of an x-ray slurry analyzer for six streams: flotation feed, middling Zn feed, copper final concentrate, lead final concentrate, zinc final concentrate, and final tailings.
• Installation of a mechanical rod feeder for the primary rod mill.
• Installation of 5 DR-180 cells in the second Zn cleaning flotation stage and 4 DR-180 cells in the third Zn cleaning flotation stage.
• Installation of 10 DR-180 cells in the bulk cleaning flotation stage, arranged in three banks (first cleaning stage with 5 cells, second with 3 cells, third with 2 cells), increasing flotation retention time from 9 minutes to 17 minutes.

Grinding and Flotation

Both circuits have a flotation feed target of approximately P80 = 104 micrometers, which is monitored manually using a Marcy scale. The concentrator flowsheet is described as conventional. Mine haulage trucks deliver polymetallic and oxide mineralized material to dedicated coarse mineralized material bins. A single crushing plant batches material to dedicated bins for each processing line.

Concentrate Production and Quality

From January 2019 to March 2021, the polymetallic circuit produced lead, copper, and zinc concentrates. Reported average concentrate grades and production details for this period include:

For lead concentrate, quality reached consistent and commercial grade averaging 57.3% lead. Gold grade in lead concentrate averaged 2.2 grams per tonne, which may trigger credit payments. Silver grade in lead concentrate averaged 1,166 grams per tonne, likely triggering credit payments. Copper grade averaged 2.2%, likely triggering minor penalty charges. Zinc grade averaged 5.4%, likely triggering penalty charges. Arsenic grade averaged 0.12%, below the typical penalty threshold.

For copper concentrate, the mass pull averaged 2.6% over the period. Copper grade in concentrate averaged 1.8%. Gold grade in copper concentrate averaged 2.3 grams per tonne, ranging from 2.25 g/t up to 2.84 g/t. Silver grade averaged 612 grams per tonne. Lead grade in concentrate averaged 0.6%. Zinc grade averaged 6.9%, likely triggering penalty charges. Arsenic grade averaged 2.45%, above the typical threshold for penalty payments.

Global recovery to concentrates for the period January 2019 to March 2021 reached 24.8% gold, 80.2% silver, 95.7% lead, 92.8% copper, and 96.4% zinc. Total concentrate production for the period was 287,535 tonnes, representing an 11.4% mass pull. Zinc concentrate accounted for 6.5% of mass pull, copper concentrate 2.6%, and lead concentrate 2.3%.

Consumables

The 2020 consumables statistics for the polymetallic circuit, in kilograms per tonne of fresh feed, include: zinc sulfate (S04Zn) at 0.75, sodium cyanide (NaCN) at 0.333, Z-11 at 0.033, MIBC at 0.053, lime at 0.666, copper sulfate (CuSO4) at 0.566, sodium metabisulfite at 0.2, Z-14 at 0.033, and zinc oxide at 0.166. Grinding media consumption included steel balls 1.5 inch diameter at 0.333 kg/t, steel balls 2 inch diameter at 0.466 kg/t, and steel rods 3 inch diameter at 0.4 kg/t.

Key reported parameters

Technical qualifications

The report notes that copper concentrate production showed a sustained drop starting June 2021. For 2020, the polymetallic circuit operated at an average of 3,040 tonnes per day of fresh feed, based on 365 days per year. Production in certain months of 2020 was affected by the Covid-19 pandemic, and other months were affected by a strike at the mine. No arsenic grade data was available for lead concentrate for 2021.

Source: Yauricocha Technical Report PEA, February 2022, Section 17: Recovery Methods.