ATERRA Reports Totora Cu/Au Project Drilling Returns 284 m Grading 0.64% CuEq Including 180 m at 0.71% CuEq

ATERRA Metals Inc. (CSE: ATC) (OTCQB: CSSCF) ("ATERRA") is pleased to report Phase I drill assay results from its Totora CuAu Project located in the Dos Amigo Mining District, 15 kilometres south of Tintina Mines' Domekyo Sulfurous development project.

Highlights

• AFROD01 returned 284 metres grading 0.64% copper equivalent ("CuEq") from surface at the Frontera Cu/Au Deposit (0.41% Cu and 0.27 grams per tonne ("g/t") gold) 

  • including 180 metres grading 0.71% CuEq (0.48% Cu and 0.28 g/t Au)

  • including 70 metres grading 0.82% CuEq (0.56% Cu and 0.32 g/t Au)

• ATOD01 returned 194 metres grading 0.41% CuEq (0.35% Cu and 0.11 g/t Au) collared on the Totora Porphyry

• Drilling confirmed the presence of significant copper and gold mineralization at both the Frontera Deposit and nearby Totora Cu/Au Porphyry highlighting the potential of the Totora Cu/Au Project

NOTES: Intervals were composited using a 0.25% CuEq cut-off grade including no more than 10-metres of internal sub-0.25% CuEq material. Intervals represent downhole lengths as insufficient data is available to estimate true widths. See "NI 43-101 Disclosure" section in this release for details on the CuEq grade calculation.

"The assay results from our Phase I drill program are impressive with drill holes confirming that both the Frontera and Totora copper-gold porphyries have the potential to host significant mineral resources," said Carl Hansen, CEO of ATERRA. "The Totora Project lies in the Dos Amigo Mining District which benefits from excellent regional infrastructure, low elevations and proximity to water. Considering these benefits, the District has seen significant interest with the recent Sumitomo / Gignac family investment in Tintina Mines, with their Domekyo Sulfurous development project, and Hot Chili's La Verde Cu/Au discovery. With all our drill assays returned, we will engage an independent consulting firm to prepare a 43-101 compliant mineral resource, comprising the Frontera, Totora and Clinton porphyries, and add the Totora Copper Gold Project to the list exciting developments in the Dos Amigo Mining District."

Totora Cu/Au Project Phase I Drill Program

ATERRA's Phase I drill program comprised a total of 2,745.5 metres of drilling targeting the Frontera Deposit, the advanced Totora Cu/Au porphyry and early-stage Algarrobilla Cu/Au porphyry. The advanced Clinton Cu/Au porphyry was not drilled as a significant amount of historical diamond drill core is available for review. Figure 1 shows the relative locations of the Cu/Au targets within ATERRA's Totora Project concessions.

Figure 1 - ATERRA's Totora Cu/Au Project Located in the Dos Amigo Mining District

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Frontera Cu/Au Deposit

ATERRA's Frontera Cu/Au Deposit, which remains open to depth, hosts a historical resource estimate of 16 million tonnes indicated grading 0.56% CuEq and a further 34 million tonnes at 0.54% CuEq in the inferred category (see Table 2).

As part of the Phase I drill program, ATERRA drilled a single diamond drill hole (AFROD01) into the higher-grade core of the Frontera Cu/Au Deposit. The hole returned 284 metres grading 0.64% CuEq with significant higher grade intervals including 180 metres grading 0.71% CuEq (see figure 2 and 3) and including 70 metres grading 0.82% CuEq. The results confirmed that the Frontera Cu/Au Deposit contains a core zone of higher grade Cu/Au mineralization extending from surface to depth.

ATERRA's upcoming Phase II drill campaign will focus on growing Frontera's resources as well expanding the current limits of the higher grade Cu/Au core zone. In addition, infill drilling will focus on increasing the confidence level of the resources with the goal of converting the current Inferred estimate to the Measured and Indicated category.

Figure 2 - Frontera Cu/Au Deposit Grade Envelope Plan (950 m Level) Highlighting AFROD01 and Historical Drill Assay Results

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Figure 3 - Frontera Cu/Au Deposit Drill Section Highlighting AFROD01 and Historical Drilling with CuEq Grade Envelopes

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Totora Cu/Au Porphyry

At the Totora Cu/Au Porphyry (Figure 4 and 5), diamond drill hole ATOD01 was collared to intersect the main Totora mineralized porphyry confirming the presence of consistent copper and gold mineralization with 194 metres grading 0.41% CuEq starting at 254 metres downhole. The mineralization cut by ATOD01 continues to surface and remains open to depth.

In addition, 6 holes were drilled to test for extensions of the mineralization at the Totora Cu/Au Porphyry. A mineralized SW extension of the main Totora Porphyry was cut in holes ATOR03A, ATOR04/4D and ATOR05. Drill hole ATOD08 filled in a gap in the drilling between the main Totora Porphyry and SW extension returning 3 intervals of +0.25% CuEq (Table 1) or 82 metres grading 0.35% CuEq (0.23% Cu and 0.15 g/t Au) at a 0.2% CuEq cutoff. The results from ATOR08 suggests that Cu/Au mineralization extends from the main Totora Cu/Au Porphyry through to the SW extension.

Reverse circulation hole ATOR01 was lost at 208 metres. ATOD01 was collared at the same location as ATOR01 and drilled with a tricone bit to 200 metres where diamond drilling commenced. Drill hole ATOR02, testing the eastern margin of the porphyry, returned no significant mineralization.

Phase II drilling at Totora will focus on increasing the dimensions of the known Cu/Au mineralization as well as infilling drilling in areas where the current drilling is too widely spaced.

Figure 4 - Totora Cu/Au Porphyry Drill Plan with CuEq Grade Envelopes Highlighting ATERRA Phase 1 and Historical Drill Assays

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Figure 5 - Totora Cu/Au Porphyry Drill Long Section with CuEq Grade Envelopes Highlighting ATERRA Phase 1 and Historical Drill Assay Results

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Algarrobilla Cu/Au Porphyry

Two drill holes, ATOR06 and ATOR07, were collared into the Algarrobilla porphyry, located approximately 1 km south of the Totora porphyry. ATOR06 returned two intervals of above cutoff grade CuEq mineralization as noted in Table 1, however, ATOR07 returned no significant mineralization. During Phase II exploration, a deep penetrating geophysical survey may be completed over the Algarrobilla Porphyry to develop target along the mineralized trend.

Drill Program QA/QC Disclosure

Phase 1a drill holes were completed using the RC technique, collared with a 5 ½" diameter bit and maintaining a consistent diameter throughout. Rock cuttings were lifted to surface by compressed air and collected from the cyclone (or hydraulic cyclone for wet samples) into the splitter by the drill contractor, under supervision of ATERRA geologists. Samples were split twice, producing the laboratory sample, a twin, and a coarse reject. Each sample was weighed, bagged, and ticketed according to a pre-prepared sampling list. Chip boxes were generated during sample extraction. Sealed sample bags were securely stored before dispatch to laboratory facilities, accompanied by reference materials (standards) for QA/QC verification. Quick chip logging was performed in the field, while RC chip trays were later sent to IMG facilities in Vallenar for detailed logging and secure storage.

Phase Ib drill holes were completed using HQ drill bits. Drill core was extracted from core tubes by the contractor and placed in core boxes with depth markers. ATERRA geologists performed quick logging at site and marked the core at 2 m intervals, adding a cut line to guide sawing. Core was cut longitudinally in half using a diamond saw; one half was bagged, ticketed, and sealed for laboratory dispatch, while the other half was returned to the core box. Core boxes were stacked on pallets, plastic-wrapped, and shipped to secure storage in IMG facilities, Vallenar. After cutting, the core was logged in detail to complement the initial quick log.

Both RC and diamond drill samples were transported to the AGS Cotecna laboratory in Coquimbo for mechanical preparation and chemical analysis. Preparation followed P70-2EN (drying at 105°C, crushing to 70% passing #10, riffle splitting to 500 g, pulverizing to 95% passing #150, two envelopes).

Gold was analyzed by Au-FA30 (fire assay, 30 g charge, AAS finish, detection limit 0.005-10 g/t). Copper was analyzed by CuTD-1ELE (four-acid digestion, AAS finish, detection limit 0.001-5%). Silver and molybdenum were analyzed as secondary elements under METD-2ELE (same digestion, Ag: 1-100 ppm, Mo: 1-1000 ppm). QA/QC results indicated no data quality issues.

Research Capital Advisory Agreement

On March 26, 2026, ATERRA announced that it had engaged Research Capital Corporation ("RCC") as a financial advisor for a period of 3 months. In consideration of RCC's engagement, ATERRA agreed to issue RCC a total of 5,750,000 common shares, to be paid in 3 monthly tranches. The final tranche of 1,916,667 ATERRA common shares was issued to RCC on June 28, 2026. The securities were issued at a deemed price of $0.0314 per share for total deemed consideration of $ $60,183.34. The shares issued are subject to a hold period of 4 months (until September 28, 2026) as per policies of the Canadian Securities Exchange.

NI 43-101 Disclosure

Qualified Person: As defined by National Instrument 43-101 ("NI 43-101") of the Canadian Securities Administrators, the "Qualified Person" for ATERRA Metals Inc. is Francisco Bravo, a resident of Santiago, Chile. As ATERRA's Chief Geologist, Mr. Bravo is considered "not independent" as the term is defined by NI 43-101. Mr. Bravo, a Public Registered Person for Reserves and Resources N° 515, in Chile, and registered in the Colegio de Geólogos de Chile under N° 725, has reviewed and approved the technical information contained in this press release.

Copper Equivalent Estimation: Copper equivalent ("CuEq") grades were estimated using a copper price of US$4.00 per pound and a gold price of US$3,500 per ounce (US$112.53 per gram). CuEq grades are estimated using the following formula: CuEq% = (((Au grade * 0.85 * 112.53) / 4.00 / 2,204.6) * 100) + (Cu grade * 0.85).

Regulatory requirements for disclosure of CuEq grade estimates require an estimation of metallurgical recoveries in the situation where no metallurgical testwork has been completed. ATERRA estimates copper recoveries of 85% and gold recoveries of 85%. It is important to note the actual recoveries will likely vary from those used in the estimation of the CuEq grades.

Historical Results: ATERRA has not undertaken any independent investigation of any historical results from the Totora Project nor has it verified the underlying technical basis for the historical resources and drilling results. The reader is cautioned against relying on the accuracy of the historical results presented; however, ATERRA considers all historical results relevant as those results will be used as a guide to plan future exploration programs: ATERRA considers the data to be reliable for these purposes.

About ATERRA Metals Inc.

ATERRA is a mineral exploration company focused on exploration opportunities in Chile. ATERRA's team of successful exploration professionals are dedicated to the discovery of mineral deposits that can be progressed into economically viable development projects creating value for all stakeholders.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This news release contains forward-looking statements, including predictions, projections and forecasts. Forward-looking statements include, but are not limited to: plans for the evaluation of exploration properties; the success of evaluation plans; the success of exploration activities; mine development prospects; the timely of future exploration programs including Phase II drilling at Totora: and, potential for future metals production. Often, but not always, forward-looking statements can be identified by the use of words such as "plans", "planning", "expects" or "does not expect", "focus is to", "continues", "scheduled", "estimates", "forecasts", "objectives", "intends", "potential", "anticipates", "does not anticipate", or describes a "goal", or variation of such words and phrases or state that certain actions, events or results "may", "could", "would", "might", or "will" be taken, occur or be achieved.

Forward-looking statements involve known and unknown risks, future events, conditions, uncertainties and other factors which may cause the actual results, performance or achievements to be materially different from any future results, prediction, projection, forecast, performance or achievements expressed or implied by the forward-looking statements. Such factors include, among others: changes in economic parameters and assumptions; all aspects related to the timing of exploration activities and receipt of exploration results including assays; the interpretation and actual results of current exploration activities; changes in project or exploration parameters as plans continue to be refined; the results of regulatory and permitting processes; future metals prices; possible variations in grade or recovery rates; variations in the recovery rates used in the calculation of equivalent grades; failure of equipment or processes to operate as anticipated; labour disputes and other risks of the mining industry; the results of economic and technical studies; delays in obtaining governmental approvals or financing or in the completion of exploration; as well as those factors disclosed in ATERRA's publicly filed documents.

Although ATERRA has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward-looking statements, there may be other factors that cause actions, events or results not to be as anticipated, estimated or intended. There can be no assurance that forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements.

Neither the Canadian Securities Exchange nor its regulation services provider has reviewed or accepts responsibility for the adequacy or accuracy of the content of this news release.

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