Toronto, Ontario--(Newsfile Corp. - September 24, 2026) - ATERRA Metals Inc. (CSE: ATC) (OTCQB: CSSCF) ("ATERRA" or the "Company") is pleased to report a maiden Inferred Mineral Resource (the "Inferred Resource") for its Totora Copper-Gold Project (the "Totora Project" or the "Project"), located in Region III, Chile, approximately 60 kilometres south of Vallenar. The Inferred Resource was estimated by SRK Consulting (Chile) SpA ("SRK") in accordance with the CIM Definition Standards for Mineral Resources and Mineral Reserves adopted by the CIM Council, as amended (the "CIM Definition Standards"), which are incorporated by reference in National Instrument 43-101 - Standards of Disclosure for Mineral Projects ("NI 43-101").

Highlights

• Maiden Inferred Mineral Resource: 159.8 million tonnes ("Mt") grading 0.30% copper ("Cu") and 0.15 grams per tonne ("g/t") gold ("Au"), or 0.51% copper equivalent ("CuEq"), at a base-case cut-off grade of 0.20% Cu.

• Contained Metals: 1,067.3 million pounds ("Mlb") of copper and 792.9 thousand troy ounces ("koz") of gold, equivalent to 1,790.8 Mlb CuEq.

• Established Mining District: The Project is located in Chile's Dos Amigos Mining District with nearby highway and high-voltage power infrastructure.

• Multiple Porphyry Systems: The Inferred Resource comprises four near-surface copper-gold porphyry deposits: Frontera, Totora, Algarrobilla and Clinton.

• Phase II Exploration Plans: Phase II drilling is expected to focus on testing extensions to the current Inferred Resource, increasing drill density and obtain samples for metallurgical testing. Untested Cu-Au targets within the Project boundaries will also be examined.

ATERRA's Totora Project lies within Chile's Dos Amigos Mining District, approximately 15 kilometres south of Tintina Mines' Domeyko Sulfuros project, 15 kilometres southwest of Hot Chili's La Verde discovery and adjacent to Compañía Minera del Pacífico's Pajonales copper-gold deposits (figure 1). The Project comprises the Taruca, Clinton, Frontera and Sevilla properties and is located near the Pan-American Highway (Highway 5) and high-voltage power infrastructure, at relatively low elevation and near potential water sources.

Carl Hansen, ATERRA's CEO, said: "This maiden Inferred Mineral Resource is an important milestone for ATERRA and the Totora Project. Since finalizing our option agreements earlier this year, we have integrated a substantial body of historical drilling with the results of our Phase I program to establish an Inferred Mineral Resource of 159.8 million tonnes containing more than one billion pounds of copper and approximately 793,000 troy ounces of gold. The historical work provided a strong starting point, while our Phase I drilling provided important confirmatory geological and assay information and improved our understanding of where the mineralized systems may extend.

"Our next step is Phase II. We intend to focus on testing potential extensions of the Frontera deposit and its higher-grade copper-gold core, testing extensions of the Totora mineralized system, and completing infill drilling where increased drill density may improve confidence in the Inferred Resource. We believe there is meaningful opportunity to expand this initial Inferred Resource while continuing to evaluate the broader Totora Project."

Inferred Mineral Resource

The Inferred Resource comprises the Frontera, Totora, Algarrobilla and Clinton copper-gold porphyry deposits. Frontera occurs on the Frontera property, Clinton on the Clinton property, and Totora and Algarrobilla on the Taruca property. ATERRA and historical drilling completed to date supports an Inferred Mineral Resource of 159.8 Mt grading 0.30% Cu and 0.15 g/t Au, or 0.51% CuEq, at a base-case cut-off grade of 0.20% Cu, containing 1,067.3 Mlb Cu and 792.9 koz Au.

Table 1 – Totora Cu-Au Project Inferred Mineral Resource (0.20% Cu Cut-Off)

* Notes:

1. The independent qualified person for the Inferred Resource, as defined by NI 43-101, is Joled Nur, CCCRRM-Chile, of SRK. The Inferred Resource has an effective date of September 24, 2026.
2. The resource estimate is classified entirely in the Inferred category. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. Inferred Mineral Resources are subject to a high degree of uncertainty, and there is no assurance that any part of an Inferred Mineral Resource will be converted to an Indicated or Measured Mineral Resource or to a Mineral Reserve.
3. Tonnages are reported in metric tonnes and metals are reported in imperial pounds and troy ounces. Figures have been rounded to reflect the precision of the estimate; totals may not sum exactly due to rounding.
4. Mineral Resources are reported at a base-case cut-off grade of 0.20% Cu. Cut-off-grade sensitivity cases are shown in Table 2; those sensitivity cases are not reported Mineral Resources.
5. The inferred resource was estimated using the following conditions: metal prices of US$4.00/lb copper and US$3,650/oz gold; metallurgical recoveries of 85% for copper and 85% for gold; mining costs of US$1.43/t mined; processing costs of US$11.30/t processed; general and administrative costs of US$2.87/t processed; selling costs of US$5/oz gold and US$0.418/lb copper; and a 10% discount rate.
6. No metallurgical testing has been completed on the Mineral Resources. Actual recoveries established through future metallurgical test work may differ from the assumed recoveries.
7. Bulk density was estimated by deposit and mineralization type: 2.62 t/m³ (Frontera oxide), 2.67 t/m³ (Frontera secondary sulphide) and 2.73 t/m³ (Frontera primary sulphide); 2.45 t/m³ (Totora and Algarrobilla oxide) and 2.67 t/m³ (Totora and Algarrobilla sulphide); and a global average of 2.65 t/m³ at Clinton, where no site-specific density determinations were available.
8. Copper equivalent was calculated using the formula: CuEq (%) = Cu (%) + [Au (g/t) × (Au price (US$/oz) ÷ 31.1035) × 85%] ÷ [22.0462 × Cu price (US$/lb) × 85%].

Cut-Off Grade Sensitivity

In addition to the base-case cut-off grade of 0.20% Cu, cut-off grades of 0.15% Cu, 0.18% Cu and 0.25% Cu were applied to the resource model to illustrate the sensitivity of tonnage, grade and contained metal to changes in cut-off grade. The 0.15% Cu cut-off case contains approximately 70% more tonnes than the base case, with an approximately 17% lower average CuEq grade. The sensitivity cases are provided for comparison only and are not reported Mineral Resources.

Table 2 – Cut-Off Grade Sensitivity Summary* (Base Case – 0.20% Cu)

* Notes: See the notes to Table 1 and the Technical Disclosure section of this news release. Only the 0.20% Cu base case is reported as a Mineral Resource. The 0.15% Cu, 0.18% Cu and 0.25% Cu cases are sensitivity cases for comparison only and must not be interpreted as Mineral Resources.

Figure 1. Location of ATERRA's Totora Cu-Au Project and other Significant Projects in the Dos Amigos Mining District, Atacama Region, Chile. Third party resource and drill assay data is from corporate and other publicly available sources.

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Geology of the Totora Project Deposits

Copper-gold mineralization across the Project is hosted by Cretaceous dioritic porphyries and associated breccias within a northeast-southwest structural corridor. The porphyries are related to quartz diorite and dioritic intrusions associated with the Domeyko Intrusive Complex, intrude Jurassic sedimentary and volcanic rocks, and are closely associated with regional northeast-southwest fault structures. Sulphide mineralization dominants the four deposits with only a minor oxide component at surface. The principal copper mineral comprising the Inferred Resource is chalcopyrite, with occasional bornite in the Frontera deposit, associated with potassic alteration and stockworks of A- and B-type veins.

Frontera Deposit (figure 2) – Diamond drill hole AFROD01 confirmed a mineralized quartz diorite porphyry with potassic alteration and returned 284 metres grading 0.77% CuEq from surface (0.41% Cu and 0.27 g/t Au). The results confirmed that the deposit contains a core zone of higher-grade copper-gold mineralization extending from surface to depth. The deposit remains open to depth.

Figure 2. Frontera Cu-Au Deposit – 3D Inferred Mineral Resource CuEq Model 

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Totora and Algarrobilla Deposit (figure 3) – Historical and Phase I drilling at the Totora deposit outlined a structurally controlled mineralized system traced for more than 800 metres along surface and to depths of up to 500 metres downhole. ATERRA reverse-circulation and diamond drilling confirmed altered quartz diorite with locally disseminated pyrite and chalcopyrite associated with quartz veining and moderate to strong potassic alteration. Diamond drill hole ATOD01 returned 194 metres grading 0.50% CuEq (0.35% Cu and 0.11 g/t Au) from 254 metres downhole. Mineralization continues toward surface and remains open at depth. A mineralized southwest extension was intersected in holes ATOR03A, ATOR04/4D and ATOR05. Hole ATOD08 filled part of the gap between the main porphyry and that extension, returning 82 metres grading 0.43% CuEq (0.23% Cu and 0.15 g/t Au) at a 0.20% CuEq compositing cut-off grade.

The Algarrobilla porphyry lies approximately 1 kilometre south of the Totora porphyry. Historical drilling outlined a 700-metre mineralized corridor and drilling remains wide-spaced. Sulphide mineralization, primarily pyrite and chalcopyrite, was observed in Phase I drill holes. Gold grades at Algarrobilla were relatively low compared to those encountered at the other 3 deposits reported.

Figure 3. Totora and Algarrobilla Cu-Au Deposits – 3D Inferred Mineral Resource CuEq Model

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Clinton Deposit (figure 4) – The Clinton copper-gold porphyry is hosted within an altered quartz diorite intruded along the regional Pajonales Fault, the same structure along which the Frontera Deposit was emplaced. The deposit is a confined pipe-shaped body extending from surface to depths of over 400 metres and remaining open to depth. ATERRA did not undertake any drilling on Clinton during its Phase I program; however, during 2018-2019, Sociedad Química y Minera de Chile S.A. drilled 6,194 metres.

Figure 4. Clinton Cu-Au Deposit – 3D Inferred Mineral Resource CuEq Model

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Key Assumptions, Parameters and Methods

The Inferred Resource was estimated separately for the Frontera, Clinton and combined Totora-Algarrobilla deposits. Copper and gold grades were estimated using ordinary kriging, and bulk density was estimated using inverse-distance interpolation, within block models regularized to 10 × 10 × 10 metre parent blocks (from 2.5 × 2.5 × 2.5 m sub-cells). The estimates used a minimum of two drill holes and five to six search passes. High-grade outliers were capped based on a variability analysis of relative error on log-probability plots.

At Frontera, the block model (1,300 m east × 1,500 m north × 1,100 m elevation) was estimated from a composite database of 51 drill holes totalling 16,519.1 metres (database closed August 20, 2026), using three mineralization domains (oxide, secondary sulphide and primary sulphide) together with lithology, albite alteration zones, and 0.1% and 0.3% total copper isograde shells, combined into eight copper-gold estimation units and seven density estimation units; bulk density was estimated by zone at 2.62 t/m³ (oxide), 2.67 t/m³ (secondary sulphide) and 2.73 t/m³ (primary sulphide, which hosts the majority of the mineralization).

At Clinton, the block model (800 m east × 600 m north × 1,000 m elevation) was estimated from a composite database of 17 drill holes totalling 6,412.5 metres (database closed July 27, 2026), using three lithological domains and a 0.1% total-copper isograde shell combined into three copper-gold estimation units. No site-specific density determinations were available at Clinton, and a global average bulk density of 2.65 t/m³ was applied.

At Totora and Algarrobilla, the block model (1,530 m east × 1,740 m north × 900 m elevation) was estimated from a composite database of 64 drill holes totalling 20,729.3 metres (database closed September 7, 2026), using two mineralization domains (oxide and primary sulphide), lithology and a 0.1% total-copper isograde shell, combined into six copper estimation units, four gold estimation units and six density estimation units. Bulk density was estimated by zone at 2.45 t/m³ for oxide material and 2.67 t/m³ for sulphide material, which hosts most of the mineralization.

The Inferred Mineral Resource was estimated using metal prices of US$4.00/lb copper and US$3,650/oz gold; metallurgical recoveries of 85% for copper and 85% for gold; mining costs of US$1.43/t mined; processing costs of US$11.30/t processed; general and administrative costs of US$2.87/t processed; selling costs of US$5/oz gold and US$0.418/lb copper; and a 10% discount rate. The Inferred Resource is reported above a cut-off grade of 0.20% Cu. The Qualified Person considers these assumptions appropriate for the deposits.

Classification of the resource in the Inferred category reflects the locally wide and irregular drill spacing, the limited amount of ATERRA drilling, the prevalence of historical drill-hole data, and the absence of metallurgical and geochemical data. On this basis, the Mineral Resource has been classified entirely in the Inferred category.

Technical Disclosure

Qualified Persons: Joled Nur, Registered Member of the Comisión Calificadora de Competencias en Recursos y Reservas Mineras (RM CMC), Registration No 181, of SRK is the independent qualified person for the Inferred Resource, as defined by NI 43-101. The Inferred Resource has an effective date of September 24, 2026. Mr. Nur has reviewed and approved the scientific and technical information in this news release relating to the Inferred Resource.

Sophia Bascuñán, Registered Member of the Comisión Calificadora de Competencias en Recursos y Reservas Mineras (RM CMC), Registration No 518, of SRK is the independent qualified person responsible for the geological modelling and verification of the data underlying the Inferred Resource, including the quality-assurance and quality-control ("QA/QC") information. Ms. Bascuñán reviewed ATERRA's Phase I QA/QC procedures and the available QA/QC documentation for historical drilling and considers the data adequate for the purpose of estimating Mineral Resources.

Francisco Bravo, a resident of Santiago, Chile and the Company's Chief Geologist, is a qualified person as defined by NI 43-101 and has reviewed and approved the remaining scientific and technical information in this news release. Mr. Bravo is not independent of the Company within the meaning of NI 43-101. Mr. Bravo is a 'Competent Person' registered with the Comisión Calificadora de Competencias en Recursos y Reservas Mineras, Registro N° 51' and is registered with the Colegio de Geólogos de Chile (No. 725).

Data Verification and QA/QC: Sophia Bascuñán carried out the verification of the available data. She reviewed all the available background, databases, quality control results and the available certificates of the historical data and the data produced by ATERRA. When available, the comparison of analytical certificates was made with the resource database for Clinton and Totora-Algarrobilla. In the case of Frontera, the review was made based on the reports made by Hot Chili as no assay certificates or QAQC data was available. For Frontera, data was available only for the hole, AFROD01, drilled by ATERRA in 2026. On September 21, 2026, Sophia Bascuñán and Francisco Bravo visited the projects, verifying more than 10% of the existing collars in each project. In October, second site visit is planned for the review of the core stored at Vallenar and Quebrada Seca storage facilities.

ATERRA completed both diamond and reverse-circulation ("RC") drilling on the Totora Project. RC holes were drilled using a 5½-inch-diameter bit. Rock cuttings were lifted to surface by compressed air and collected from the cyclone, or a hydraulic cyclone for wet samples, into the splitter by the drilling contractor under the supervision of Company geologists. Samples were split twice to produce a laboratory sample, a twin sample and a coarse reject. Each sample was weighed, bagged and tagged using a pre-prepared sampling list. Chip boxes were generated during sample extraction. Sealed sample bags were stored securely before dispatch to the laboratory, with certified reference materials inserted for QA/QC monitoring. Preliminary chip logging was completed in the field; RC chip trays were then sent to IMG facilities in Vallenar for detailed logging and secure storage.

Diamond holes were drilled using HQ core. The drilling contractor extracted the core from the core tube and placed it in core boxes with depth markers. ATERRA geologists completed preliminary logging at site and marked the core at two-metre intervals, including a cut line to guide sawing. Core was cut longitudinally using a diamond saw; one half was bagged, tagged and sealed for laboratory dispatch, and the other half was returned to the core box. Core boxes were stacked on pallets, wrapped and shipped to secure storage in Vallenar. Detailed geological logging followed.

RC and diamond-drill samples were transported to the AGS Cotecna laboratory in Coquimbo for mechanical preparation and chemical analysis. Preparation followed method P70-2EN: drying at 105°C, crushing to 70% passing a No. 10 screen, riffle splitting to 500 grams, and pulverizing to 95% passing a No. 150 screen. Gold was analyzed using method Au-FA30 (30-gram fire assay with an atomic-absorption finish; detection range 0.005-10 g/t). Copper was analyzed using method CuTD-1ELE (four-acid digestion with an atomic-absorption finish; detection range 0.001-5%). Silver and molybdenum were analyzed as secondary elements using method METD-2ELE (four-acid digestion; Ag detection range 1-100 ppm and Mo detection range 1-1,000 ppm). The QA/QC review identified no material data-quality issues.

Historical drilling data used in the Inferred Resource were derived from sources that the Company and SRK consider reliable. The Company has not independently verified every item of historical information; however, Ms. Bascuñán reviewed the available QA/QC documentation and considers the data adequate for the purpose of estimating Mineral Resources. The supporting NI 43-101 technical report will describe the historical data and SRK's verification procedures in greater detail.

Copper Equivalent: Copper-equivalent grades are reported for comparative purposes and were calculated as follows:

CuEq (%) = Cu (%) + [Au (g/t) × (Au price (US$/oz) ÷ 31.1035) × 85%] ÷ [22.0462 × Cu price (US$/lb) × 85%]

The calculation uses metal prices of US$4.00/lb copper and US$3,650/oz gold and assumes recoveries of 85% for copper and 85% for gold. The individual copper and gold grades used to derive CuEq grades are reported with the CuEq grades. Molybdenum and silver were not included in the CuEq calculation. It is reasonably expected that all metals included in the calculation could be recovered and sold.

Factors That May Materially Affect the Mineral Resource: The Inferred Resource is subject to factors that could materially affect potential development of the Project. The Company holds its interests in the properties comprising the Totora Project under option agreements that require future payments and, in certain cases, exploration commitments to maintain or increase its interests. Failure to satisfy an applicable option requirement could result in the Company losing some or all of its interest in the applicable property.

No metallurgical test work has been completed on the Mineral Resources. The recoveries used in the Inferred Resource are assumptions, and recoveries established through future metallurgical test work may differ. The Inferred Resource is also sensitive to metal prices, operating costs and other economic assumptions used to establish RPEEE. Potential development of the Project may also be affected by water and infrastructure availability, permitting and environmental requirements, surface and mineral tenure, community matters, and changes in applicable Chilean laws and regulations.

Technical Report

A technical report prepared in accordance with NI 43-101 and Form 43-101F1 and supporting the Inferred Resource will be filed on SEDAR+ at www.sedarplus.ca and on the Company's website within 45 days of this news release. The technical report will contain the complete assumptions, parameters and methods underlying the Inferred Resource. This news release is a summary only.

About ATERRA Metals Inc.

ATERRA Metals Inc. is a mineral exploration company advancing copper-gold projects in Chile. The Company's flagship Totora Copper-Gold Project is located in the Dos Amigos Mining District of Region III, Chile, approximately 60 kilometres south of Vallenar. The Project comprises the Taruca, Clinton, Frontera and Sevilla properties and hosts the Frontera, Totora, Algarrobilla and Clinton copper-gold porphyry systems, together with earlier-stage exploration targets. The Company holds its interests in the Project under option agreements and has no Mineral Reserves on any of its properties.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This news release contains "forward-looking information" within the meaning of applicable Canadian securities legislation. Forward-looking information is generally identifiable by words such as "anticipates", "believes", "expects", "intends", "plans", "potential", "may", "will", "could", "should" and similar expressions, or statements that certain events or conditions "will" or "may" occur. Forward-looking information in this news release includes, but is not limited to, statements regarding the potential size, continuity and expansion of the mineralized systems at the Totora Project; the potential to expand the Mineral Resources through additional drilling and to convert Inferred Mineral Resources to higher-confidence categories; the timing, scope and objectives of the Company's planned Phase II exploration program; the potential for Phase II drilling to extend mineralization at Frontera, Totora, Algarrobilla and other targets within the Project and to further define higher-grade portions of the mineralized systems; the potential for additional discoveries within the Totora Project; planned metallurgical testwork and the potential recoverability of copper and gold; and the anticipated filing of an NI 43-101 technical report supporting the Inferred Mineral Resource within 45 days of this news release.

The Inferred Mineral Resource and forward-looking information contained in this news release are based on a number of assumptions that the Company and the Qualified Persons consider reasonable as of the date hereof, including assumptions regarding geological and grade continuity between drill holes; metal prices of US$4.00/lb copper and US$3,650/oz gold; metallurgical recoveries of 85% for copper and 85% for gold; the mining, processing and other cost assumptions used in establishing reasonable prospects for eventual economic extraction; the Company's ability to obtain financing on acceptable terms and to fund its planned exploration activities; the Company's ability to make required option payments and satisfy applicable exploration commitments; the availability of equipment, personnel and contractors required to carry out Phase II exploration; and the ability to obtain and maintain the concessions, surface rights, water rights, permits and other authorizations required for exploration and potential future development.

Forward-looking information is subject to known and unknown risks, uncertainties and other factors that may cause actual results to differ materially from those expressed or implied by such forward-looking information. Such risks include, but are not limited to: the inherent uncertainty of Mineral Resources, particularly Inferred Mineral Resources; the possibility that future drilling will not confirm the geological interpretations, grades, tonnages or continuity reflected in the Inferred Mineral Resource; the possibility that additional drilling will not expand the Mineral Resources or result in conversion of Inferred Mineral Resources to higher-confidence categories; the risk that Phase II drilling may be delayed, modified or not completed as currently contemplated, or may not produce the results anticipated; the possibility that mineralization identified outside the current Mineral Resource ultimately will not satisfy the requirements for inclusion in a Mineral Resource; metallurgical recoveries determined through testwork may differ materially from the recoveries assumed in the Inferred Mineral Resource; copper or gold prices may be lower, or mining, processing and other costs higher, than those assumed; the Company may be unable to obtain sufficient financing or satisfy payments and other obligations under its property option agreements; and risks associated with title and tenure, water availability, permitting and environmental approvals, community relations, infrastructure and changes in Chilean laws, regulations, taxation or royalty regimes.

Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. Inferred Mineral Resources are subject to a high degree of uncertainty as to their existence and as to their economic and legal feasibility, and there can be no assurance that any part of an Inferred Mineral Resource will be upgraded to a higher-confidence Mineral Resource category or converted to a Mineral Reserve. Exploration results and indications of mineralization outside the current Mineral Resource do not constitute a Mineral Resource, and there can be no assurance that further exploration will result in the definition of additional Mineral Resources.

Although the Company has attempted to identify important factors that could cause actual results to differ materially from those contained in forward-looking information, there may be other factors that cause results not to be as anticipated, estimated or intended. Readers are cautioned not to place undue reliance on forward-looking information. The forward-looking information contained in this news release is made as of the date hereof, and the Company undertakes no obligation to update or revise such information except as required by applicable securities laws.

Neither the Canadian Securities Exchange nor its Market Regulator (as that term is defined in the policies of the Canadian Securities Exchange) accepts responsibility for the adequacy or accuracy of this release.

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Source: ATERRA Metals Inc.