Big River Gold : ECE Study Update and Expansion PFS

ASX RELEASE

1 April, 2021

BIG RIVER UPDATES COST ESTIMATES FOR 2MTPA BORBOREMA PROJECT

AND COMMISSIONS PFS FOR POSSIBLE LARGER PROJECT

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Big River Gold Limited (ASX:BRV) (Big River or Company) is pleased to announce the results of its Engineering Cost Estimate study (ECE) updated for its 2 million tonnes per annum (Mtpa) Borborema gold project (Project) in Brazil.

Big River is also pleased to announce that it has commissioned a pre-feasibility study (PFS) for an expanded production rate and has advanced the status of its infrastructure development and land access acquisition for the Project.

1. ECE update

The ECE update was conducted by internationally experienced and recognised engineering consultants, GR Engineering Services (GRES), with the purpose of updating the capital costs developed for the 2019 Definitive Feasibility Study as updated in 2020 and 2021 (DFS)1 while retaining the other fundamental assumptions including mine/plant scheduling, pit design, mining contractor equipment, process path and use of process water which was outlined in the DFS. Operating costs were updated by Big River's Owners

Team with assistance from independent consultants.

The updated DFS study reported to the ASX on 9 July 2020 was reviewed in 2021 to assess the most effective use of capital and the currency of the cost basis assumed. The first part of this review was an Option Study, which was a precursor to this ECE update, the results of which were reported to the ASX on 30 March 2021.

These were sufficiently encouraging to warrant completing the exercise with costs in the ECE updated for 2022 conditions. Most operational and economic assumptions remained the same as for the DFS and Option Study, with the material exceptions noted below.

1 Refer (1) ASX announcement 23 December, 2019; (2) ASX announcement 9 July, 2020 and (3) ASX Announcement 30 March, 2021

• 1. A concessional corporate tax rate is available to the Project due to its location in north east Brazil making it eligible for Sudene concession reduction. Social Contribution tax remains unchanged.

• 2. Capital and operating costs have been updated to include Q3/2021 and some Q1/2022 estimates derived from supplier and service provider quotes, estimates from comparable operations and current pricing of steel.

• 3. Process path and key plant components remain the same but ongoing engineering identified options in available plant that would provide operating improvements (e.g., Single stage crushing, SAG plus ball mill versus only ball mill, AARL rather than Zadra elution circuit) as well as oversizing the crushing and tails thickening circuits in anticipation of increasing future throughput via an expansion. Some plant not previously included in the DFS was identified as providing benefits and added to the engineering design where it had short payback periods and/or provided operating cost savings and/or improved operational efficiency or security (e.g., gravity gold recovery circuit and cyanide recovery thickener). In addition, the footprint of earthworks was increased to accommodate possible future expansions.

• 4. Increase in Owners and Pre-production costs partly due to reallocation from Plant capex and partly due to the omission or understatement of items in several cost areas of the DFS. Also includes mining pre-production costs that were reported but previously assigned to working capital.

• 5. Pre-production capital costs and do not include sustaining or working capital costs.

• 6. Contract mining to same pit design defined in the DFS.

• 7. An increase in works for water management including upscaling of the waste water pipeline to improve flow, additional maintenance and inclusion of pumps at the Currais Novos sewage works and improvement of water catchments and dams on site.

• 8. GRES recovery adjustments based on its testwork review and process design basis.

For a side-by-side summary of all studies completed, see Table 3 in the body of the announcement. Note that the 2021 Option Study was the first part and precursor to the final ECE update in 2022 which updated costs and prices.

The ECE update has been delayed by difficulties in obtaining prices and quotes for equipment and services in the current environment which mixes the impact of a mining boom and COVID. As a result, the ECE accuracy level is lower than preferred at ±20% - 25%.

Results of the ECE update confirm a significant increase in the estimated plant and infrastructure cost from US$69.5 million to US$115.2 million (excluding owner's costs and contingency).

These cost increases are predominantly associated with supply chain issues, increases in the cost of equipment and services, upscaling project capacity and layout, and the addition of previously unpriced capital items with short payback benefits.

At the same time, owner's costs and pre-production expenses were updated by independent consultants Macromet and Mining Focus Consultants Pty Ltd (Mining Focus) with the new estimated total being US$29.9 million including a contingency of US$6.9 million, which differs from the total US$6.6 million adopted in the DFS.

GRES, Macromet and Mining Focus have consented to be named in this announcement and for the content of the ECE updates and studies to be extracted and summarised in this announcement.

Total capital costs are now estimated at US$174.0 million, including contingencies and estimating allowances of US$19.8 million.

The Company updated its 2Mtpa Financial Model base case with the above results at a constant gold price of US$1,600/oz (versus the $1,550/oz used previously).

The base case results, along with a US$1,800/oz gold price scenario for comparative purposes, reveal the following key metrics:

With the results of recent site water balance studies suggesting the easing of process water limitations, an investigation into higher throughput production rates was considered justified in addition to the Stage 1 update.

The results of the process water investigations were highly encouraging and in line with the original 2013 plan to mine the 1.6 Moz gold reserve at a rate of 4Mtpa.

2. Possible Expansion of Plant Size and progress to Pre-Feasibility Study

The results of the water studies for the 2 Mpta Project led to the Company exploring a Project with a larger annual throughput, which was originally the plan a number of years ago. The Big River Board was encouraged by the initial internal modelling results and has commissioned GRES to undertake a PFS for a Project with a higher production rate design. The Company will update the market as and when the PFS has been delivered, noting that this work is scheduled for completion in the second quarter of 2022.

3. Land Access Acquisition

The Company is pleased to report that land access acquisition to establish the 69kV power line from Currais Novos to site, is well advanced.

Executive Chairman, Andrew Richards, commented:

"We are very pleased with the long-term future of the project including the potential for higher throughput rates which could better reflect the original plan for the Borborema Project. This would show a more efficient use of capital and better optimises the resource to deliver high returns over a longer period. This would not have been possible without the implications for water management identified in recent studies. While there has been a significant increase in estimated capital and operating costs, the Company is exploring more innovative ways of managing these costs."

Further details in relation to the ECE and the updated financial model for the 2Mtpa project are set out in the following pages. Appendix 1 provides details on the assumptions used in the March 2022 ECE update

For and on behalf of the Board.

Andrew Richards

Executive Chairman Big River Gold Ltd

1.DESIGN AND ENGINEERING COST ESTIMATE STUDY (ECE)

1.1 BACKGROUND

Big River wishes to advise the results of the ECE update conducted by GRES and BRV with assistance from consultants.

The ECE update was undertaken to address the design and costings of the Borborema Gold Project (BGP or Project) and its possible expansion from the DFS previously reported in December 20192 and updated in 2020 and 20213, noting that the DFS adopted an initial stage mining rate of 2Mtpa over 10 years (Stage 1). Appendix 1 includes details of the assumptions used in the March 2022 ECE update

Table 3 summarises the capital expenditure estimated for each of these studies.

The key focus of the ECE was to update the cost of services and supplies for capital and operating costs assumed in the original DFS.

In the course of that exercise, some modifications were proposed for the plant to deliver improved operation, environmental benefits and/or early payback. These are commented on below however, the mining schedules, pit design, resources and reserves were unchanged and material underlying technical assumptions of the DFS were unchanged.

In addition, limitations on production throughput due to lack of process water were alleviated following the dynamic water balance and water management studies undertaken by SRK Consultores do Brasil Ltda (SRK Brazil) reported to ASX on 2 December 2021. This led the BRV Project team to instigate a desktop study investigation into the economic benefits of higher throughput production rates.

Specifically, the findings of the SRK Brazil's dynamic water balance study and its implications for water management and security of process water supply provided the opportunity to return to the original 2013 Feasibility Study findings which envisaged a 4Mtpa operation to mine the entire 1.6 Moz Ore Reserve.

That plan was originally put on hold due to the perceived lack of water and the gold price at the time.

However, with sufficient process water now appearing available to support a larger operation, the Big River Board is commissioning GRES to undertake a PFS for a Project with a design criterion including a significantly higher annual throughput. This work is expected to be completed by the end of Q2 and the Company will update the market as and when the PFS has been delivered.

• 2 Refer ASX announcement 23 December, 2019

• 3 Refer (1) ASX announcement 9 July, 2020 and (2) ASX Announcement 30 March, 2021

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