This page was created by Thunder Gold Corp. All statements about mineral resources refer to the January 19, 2026 NI 43-101 mineral resource estimate prepared by Micon International Limited. Mineral resources are not mineral reserves and do not have demonstrated economic viability.
Gold assay results
| Gold assay results are the foundation of every resource estimate, and most investors never see the laboratory that produced them. For Thunder Gold Corp (TSXV: TGOL | OTCQB: TGOLF | FSE: Z25), the numbers that define the 3.5 Moz at the Tower Mountain gold property – 34.0 Mt Indicated at 0.46 g/t Au and 211.1 Mt Inferred at 0.45 g/t Au – rest on assaying carried out under a QA/QC programme at accredited laboratories. This page explains gold assay results and the exploration methods that produce them, from airborne surveys to the fire assay that delivers a grade. |
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How Gold Is Measured: Fire Assay and ICP
The standard method for gold assaying is fire assay. A weighed sample is fused with a flux of lead oxide, soda ash, borax and silica at around 1,000 degrees Celsius; the gold and silver collect in a lead button, which is then cupelled to remove the lead and leave a precious-metal bead that is weighed. For lower-grade material, the bead is often analysed by inductively coupled plasma, or ICP, which can measure gold to parts per billion. The result is reported in grams per tonne, g/t, the same unit used in resource estimates. Modern labs run check assays, duplicates and certified reference materials on every batch, and the data only enters a resource model after the QA/QC passes.
The QA/QC Programme Behind the Numbers
A laboratory result is only as trustworthy as the programme around it, and the standard programme inserts blanks, certified standards and duplicates into the sample stream at regular intervals – typically every 20 samples. A blank that returns gold means contamination from a previous sample; a standard that drifts outside its certified range means the laboratory’s calibration has slipped; a duplicate that disagrees with its original means the sampling was uneven. Thunder Gold’s work at Tower Mountain is underpinned by QA/QC programmes run through accredited laboratories, and the Qualified Persons who prepared the January 19, 2026 Micon International resource estimate – William Lewis, P.Geo., Charley Murahwi, P.Geo., FAusIMM, and Tudorel Ciuculescu, P.Geo. – reviewed that data. Mineral resources are not mineral reserves, and the estimate assumes a US$3,000/oz gold price.
Soil, Till and Rock Sampling
Before any drilling starts, geochemistry narrows the target. Soil and till sampling collects fine material from a grid across the property and analyses it for gold and pathfinder elements such as arsenic, antimony and bismuth. A gold anomaly in till can trace a deposit that lies beneath glacial cover, which is common in Northwestern Ontario. Rock chip and channel samples, such as the 58 surface channel samples at the A-Target that averaged 3.16 g/t Au across 20 m during the 2021-2022 programme, provide direct evidence of grade at surface. None of these methods replaces drilling, but they decide where the rig goes.
Geophysics: Mapping the System Before You Drill
Geophysical surveys map what is beneath the ground without digging. Magnetic surveys are the first tool at Tower Mountain, because the CSC alteration that hosts gold has destroyed magnetite, producing broad magnetic lows that mark where the system has been altered. Electromagnetic, induced polarisation and gravity surveys map conductive and chargeable zones, and the 2026 magnetotellurics airborne survey awarded to Tower Mountain will map structure beneath cover at depth. The value of geophysics is that a single survey covers thousands of hectares and highlights the few kilometres worth drilling, which is why the 2026 programme combines airborne surveys with 15,000-25,000 m of infill and expansion drilling.
Geological Mapping and Core Logging
Geology maps and core logs are the human layer that sits between the geophysics and the assay. A geologist walking the outcrop records the rock types, the structure and the alteration, and a core logger does the same for the cylinder of rock the drill brings up. At Tower Mountain, the key observations are the multi-phase intrusions of the Tower Mountain Intrusive Complex – syenites, monzonites, diorites and gabbro – and the CSC alteration that extends more than 500 m west of the intrusive contact. The correlation between disseminated, fine-grained pyrite and gold grade is one of the most useful relationships in the deposit, because it gives the logging geologist a real-time guide to mineralisation. View core images from the programme.
How Assay Results Become a Resource
Assay results become a resource only after a long chain of checks. The samples are logged, cut, bagged, shipped and assayed; the results are loaded into a database; the database is validated; the assays are composited; and a block model is built, typically at a cut-off grade such as the 0.19 g/t Au used in the Micon estimate, with a specific gravity of 2.77 and an open-pit optimisation at a 30-degree slope in overburden. The model is then classified into Indicated and Inferred categories depending on drill spacing and data quality. The 16 metallurgical samples tested at Bureau Veritas in 2022 and SGS Canada in 2025 returned gold recoveries of 68%-94.9%, averaging about 85%, with a Net Neutralizing Potential of 76.5 kg CaCO3 per tonne, meaning acid drainage is unlikely, and a Bond work index of about 20 kWh/t, indicating soft ore. Those numbers feed the economic parameters of the resource estimate and, later, of the initial PEA the Company is targeting for late 2026 or early 2027. Read the full results and the technical report.
Reading an Assay Certificate
An assay certificate is not a promise; it is a measurement with a stated method, a detection limit and a batch of quality-control results attached. The fire-assay figure is the headline number, but the certificate also shows the sample weight, the flux mix, the finish method and, crucially, the results of the blanks, standards and duplicates inserted by the client. A reader checking a certificate looks for three things: whether the standards fall within their certified ranges, whether the blanks stay clean, and whether duplicate pairs agree within the laboratory’s expected precision. At Tower Mountain, the assays that feed the resource database pass those checks before the Qualified Persons – William Lewis, P.Geo., Charley Murahwi, P.Geo., FAusIMM, and Tudorel Ciuculescu, P.Geo. – accept the data for use in the Micon International estimate. Read the full results and the technical report.
Frequently Asked Questions
Q: What are gold assay results?
A: Gold assay results are laboratory measurements of how much gold is in a sample, usually produced by fire assay with an ICP or gravimetric finish and reported in grams per tonne. At Tower Mountain they are generated under a QA/QC programme at accredited laboratories and feed the resource estimate.
Q: How does fire assay work?
A: A weighed sample is fused with flux at around 1,000 degrees Celsius so gold and silver collect in a lead button, which is then cupelled and weighed. Lower-grade material may be finished by inductively coupled plasma, which measures gold to parts per billion.
Q: What is a QA/QC programme in gold exploration?
A: It is the system that validates laboratory results by inserting blanks, certified standards and duplicates into the sample stream, typically every 20 samples. If a blank shows gold, or a standard drifts, the laboratory’s work is rejected.
Q: How do geophysical surveys help find gold?
A: Surveys such as magnetics map what lies beneath the ground without digging. At Tower Mountain, the CSC alteration that hosts gold has destroyed magnetite, producing broad magnetic lows that mark where to drill, and a 2026 magnetotellurics survey will map structure at depth.
Q: How do assay results become a mineral resource?
A: Assays are validated, composited and loaded into a block model built at a cut-off grade such as 0.19 g/t Au, with a specific gravity of 2.77, then classified as Indicated or Inferred depending on drill spacing and data quality. The 16 metallurgical tests with about 85% average recovery feed the economic parameters.