Finding Corundum in Ontario: Exploring Craigmont and Robillard Mountain

 

Ontario is home to some of the most fascinating corundum-bearing rocks in Canada, offering rockhounds and mineral collectors unique opportunities to find naturally occurring corundum, sapphires (but not at Craigmont). From the historic Craigmont Corundum Mine and it’s spectacular view atop Robillard Mountain to lesser-known localities like Gutz Farm and Egan Chutes, Ontario’s nepheline syenite belts host a variety of corundum expressions and a host of impressive specimens.

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These silica-poor, aluminum-rich rocks, often altered by metasomatic fluids, create ideal conditions for crystal growth, producing stubby hexagonal plates, rounded grains and pebbles, barrel-shaped corundums, and occasional gem-quality sapphires. Whether you are an experienced collector or exploring rockhounding in Ontario for the first time, understanding the geology, mineral associations, and field techniques is essential for successfully discovering corundum in the province.

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Table of Contents: Finding Corundum in Ontario – Craigmont, Robillard Mountain, and Local Mines

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1. Introduction: Rockhounding and Corundum in Ontario

2. Crossing Robillard Mountain: A Challenging Ascent for Ontario Rockhounds

3. Early Discovery of Corundum on Robillard Mountain

4. Craigmont Corundum Mine History and Early Operations

5. How the Craigmont Mine Ended

6. Visiting the Craigmont Adit and Field Site

7. Bancroft's Nepheline Syenite Belt

8. Why Nepheline Syenite Comprises most of Ontario's Corundum Mines

9. Accessory Minerals and Molybdenum at Craigmont

10. Why Corundum is often found along a Marble Contact

11. Craigmont vs Princess Sodalite Mine Geology

12. Corundum, Sapphire, and Ruby: Trace Elements and Color

13. Working Ontario Rivers for Sapphire

14. Collecting Corundum in Ontario: Tips and Localities

15. Field Guide: What to Look for in Ontario Corundum

16. FAQ: Finding Corundum and Sapphires in Ontario

    • 13.1 Where can I find corundum in Ontario?

    • 13.2 Which rivers are best for sapphire hunting?

    • 13.3 What does Ontario corundum look like?

    • 13.4 How do I spot promising rocks for corundum?

    • 13.5 Why are some crystals blue, red, or grey?

17. Corundum in Ontario: A Multi-Faceted Mineral

18. Author Bio: Michael Gordon

 

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Crossing Robillard Mountain: A Challenging Ascent for Ontario Rockhounds

 

Crossing over the top of Robillard Mountain is at times a real undertaking. Getting up there I’d struggled along precipitous paths and sweat enough to soak through everything that I was wearing. Wiping my forehead with a Tilley, I realized that it did no good. The hat had become a sopping mop, and no sooner had it cleared my face than the blackflies were in my eyes again.

After an epic struggle I found myself perched atop a lofty outlook with what they called the Klondike diggings dropping down below me. Vast meadows of delicately perched boulders spread out over terraces and steep inclines.

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Beware of the potential for avalanche. Whole sections of slope look to be easily mobilized by a stumbling rockhound and, unlike snow which suffocates, these boulders once moving would become unstoppable, In a catastrophic rumbling you’d be reduced to no more than shredded cloth and pulverized flesh. They’re syenitic boulders—not that it reduces the impact of an avalanche, but it’s nice to know that they’re low in quartz content, making them more likely to show the development of corundum crystals. After lying there for the past 120 years, the unstable boulders are now sporting an aging fluff of lichen.

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Early Discovery of Corundum on Robillard Mountain

 

Flashback to the late 1800s  when Henry Robillard and his daughter Anne crossed over the top of the mountain. Supposedly the trip was to find cranberries on the other side. It seems to make no sense as cranberries are found in bogs, but that’s the story.

 Atop the mountain, the two noticed an unusual patterning in the rock that Henry likened to cruet stoppers stacked together on end.

 

What might you ask is a cruet stopper? It’s an old-fashioned plug inserted into a hand-blown bottle, rounded at one end and multi-sided at the other—for grip, I’m told. Looking down atop the stopper, the six-sided grip emulates the six-sided prism of a corundum crystal; but they weren't gemologists they were farmers and they'd found the first and biggest of Ontario's corundum mines - 20,000 tons were extracted up until 1945.

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Back then, without a way to communicate rapidly, exchange ideas, or reach isolated places, the wheels of progress turned slowly. Specimens were walked and canoed through the verdant catchment of the Ottawa River to a place of expertise where they were identified as corundum crystals. Once it was discovered, more time was required to set in place a way to extract the ore and move it to market.

 

 

 

 

 

 

 

 

 

 

 

Craigmont Corundum Mine History and Early Operations

 

It was not until 1899 that anything really concrete took place around extraction. A.C. Craig and J.H. Shoshone acquired the property for the Canada Corundum Company, and development began the following year with a workforce of 60.

 

Concurrently, similar discoveries had been made some distance to the west at what became known as the Burgess Mine. Both Craigmont and Burgess tapped into the same nepheline syenite belt that stretches across the landscape north of Bancroft, passing through Renfrew, Hastings, and Haliburton Counties. 1898–1901 marked the area’s corundum rush, and there are at least 20 other localities in the area where corundum has been found and extracted.

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Four hundred and fifty feet above the river, I looked out over a scrubby open terrain where once the town sat. Four hundred miners worked the slopes at the mine’s peak production. At the bottom of the mountain, there was the mill and homes for 2,000 people. Restless souls had the option of escape to nearby Combermere by stagecoach three times a week. The roads once traveled by horse and carriage are still much the same, a gritty pink sand that’s likely sediment from the blasting.

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At its peak, the mine was producing 300 tons a day. It was the first and biggest of Ontario's corundum mines. Blasted off the hillsides, and pushed down the slope the ore was funneled through a series of sluices. Heading back down the slope that was once above the mill you'll see all sorts of stone abutments that were connected to the mining process. Once at the bottom of the mountain the ore was cobbed and sorted on big tables in the mill, a rambling wooden structure heated by an infamous boiler.

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How the Craigmont Corundum Mine Ended

 

One cold day, some bright spark decided to store frozen dynamite near the boiler along with blasting caps—and well, you can imagine the outcome - a spark, the fuse, dynamite doing its thing. 1913 marked the beginning of the end with the communion of the boiler and the dynamite. The resulting blast killed a blacksmith nearby who was shoeing a horse, and another local resident lost his hearing. Mill work was shuffled over to the Burgess Mine, and the decline of Craigmont dragged on until the 1950s, when synthetic product replaced natural corundum on the market.

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These central Ontario mines almost all follow this pattern of boom and then collapse. Ontario's corundum mines were no different. And for their presence in Bancroft’s giving pegmatites many reinvent themselves in unimaginable ways. Who would have thought that a mine could produce mica in the late 1800s, then apatite for phosphate, feldspars, uranium and now rare earths for green technologies.

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 There is little there today to indicate the once-thriving industry, aside from a rather photogenic rusting car and a stable on a side road nearby, inhabited by a reclusive hermit. I think he’s Russian Orthodox and seems to grow a wonderful vegetable garden in the sandy floodplain soil. Craigmont did not reinvent itself; the deposit was large and predominantly a single mineral. Most central Ontario deposits had a more diverse assemblage of minerals so when the economy changed its needs, the abandoned mines were able to accommodate for the most part.

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Visiting the Craigmont Adit and Field Site

 

Parking at the base of the mountain, I had followed along a path that soon forked. To the right, ATV trails climbed the slope; to the left, the path trailed alongside swamp and beaver dam until a ravine led up to the dripping adit. It’s an impressive site, the entrance being a great salmon-colored roof of rock, and entering it you wade through sulfurous water until you emerge on a gravelly beach. arriving in early spring you find yourself barred from entry. Thick icicles set a glassy wall in front of you and try as I might I was unable to break through. Inside the mine drill holes have become a habitat for the little brown bat, and so after taking a beating during the white-nose epidemic, the bats should be left undisturbed as best as possible.

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Toward the end of the tunnel, I began to feel a pounding headache and suspected that the air was bad, so we made a quick exit. Beyond an interesting diversion, I’d say the tunnel held no rockhounding potential.

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The York River ribbons out below, finally joining the silvery expanse of the Conroy Marsh off in an easterly direction. Much of the Mountain’s product found its way along a short rail line to the river, and from there it was transported by the colorfully named barges—Ruby, Geneva, and Mayflower—up to Barry’s Bay. It’s recorded that there were up to 20 huge cuts in the side of the mountain, as well as an adit that tapped the syenite from beneath.

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​Bancroft's Nepheline Syenite Belt

 

The nepheline syenite belt running through the Bancroft area is part of the ancient Grenville Province, specifically within the Central Metasedimentary Belt. It formed roughly 1.0–1.2 billion years ago from silica-poor, alkaline magmas that crystallized into rocks like nepheline syenite instead of typical quartz-rich granite. Today, the belt appears as a series of elongated, discontinuous bodies stretching through Haliburton, Bancroft, and into the Faraday–Cardiff area, often deformed into gneissic layers by later tectonic events.

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These rocks are mineralogically unusual because of their low silica and high alkali content, hosting minerals such as nepheline, sodalite, cancrinite, scapolite, and zircon. The belt is rarely uniform—instead, nepheline syenite is interlayered and mixed with marble, amphibolite, and other metamorphic rocks. This complex setting was further modified during the Grenville orogeny, which introduced deformation and metasomatism, allowing fluids to move through the rocks and alter their chemistry.

 

This combination of alkaline composition, deformation, and fluid activity makes the Bancroft belt especially rich in rare and unusual minerals. Chemical interaction between nepheline syenite and surrounding rocks—particularly marble—creates localized zones where minerals like sodalite or even corundum can form under the right conditions. As a result, the belt is not just a continuous mineral source, but a patchwork of highly variable environments, where small changes in chemistry and structure control what minerals appear.

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Why Nepheline Syenite Comprises most of Ontario's Corundum Mines

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Corundum forms in nepheline syenite because the rock is silica-poor but rich in aluminum. In most rocks, aluminum combines with silica to form feldspar minerals, but in nepheline syenite there isn’t enough silica available, and so as a result, the excess aluminum crystallizes instead as corundum (Al₂O₃).

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This process is often enhanced by metasomatism, where hot fluids move through the rock, removing even more silica while redistributing elements.

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At places like the Craigmont Corundum Mine, these altered zones—especially near contacts between syenite and gneiss—are where corundum is most concentrated and best developed. Finding corundum at Craigmont starts with recognizing its unusual host rocks, which are alkaline and silica-poor. The most important target is nepheline syenite or nepheline gneiss, typically light grey to buff with a slightly greasy appearance from nepheline. These rocks can contain significant amounts of corundum and are often very nepheline-rich. Corundum can also occur in scapolite gneiss, especially where the rock is pale, banded, and shows signs of alteration.

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The best places to search are “hybrid” zones where different rock types meet, particularly along contacts between pink or buff syenite and surrounding gneiss. These areas are often metasomatized (chemically altered), and that process helps concentrate corundum.

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Collectors frequently find better crystals in these transition zones rather than in uniform, unaltered rock, making them key targets when exploring dumps or exposed cuts. In the field, focus on rocks with low quartz content, coarse feldspar mixed with nepheline, muscovite “books,” dark minerals such as hornblende or pyroxene, and even garnet.

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Corundum typically appears as stubby hexagonal crystals or barrel-shaped grains in bronze, greenish, or grey tones. A practical tip is to ignore fresh-looking, quartz-rich rocks and instead target the more altered, patchy, feldspar-rich material—especially where pinkish syenite grades into pale gneiss—as this is often the most productive ground. A key rule in mineralogy is that corundum and quartz do not coexist under stable conditions, which is why corundum is always associated with silica-deficient rocks.

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Accessory Minerals and Molybdenum at Robillard Mountain

 

At the Craigmont Corundum Mine, the accessory minerals reflect the mine’s unusual alkaline, silica-poor chemistry and its later history of metamorphism and metasomatism.

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Common accessory minerals include scapolite, feldspar (orthoclase and plagioclase), nepheline, muscovite, amphiboles, and pyroxenes. Scapolite forms in calcium-rich, silica-poor environments where fluids introduce chlorine or carbon dioxide.

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Muscovite “books” often occur in altered zones where potassium and fluids have reworked the rock. Dark minerals like hornblende and pyroxene reflect the original high-temperature chemistry of the intrusion, while garnet may appear in zones that experienced stronger metamorphism. These minerals are essentially the “supporting cast” that indicate the same geochemical conditions that allow corundum to form.

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Molybdenite (MoS2) at Craigmont occurs because the nepheline syenite there is an alkaline, silica-poor intrusive that concentrates incompatible elements like molybdenum in its late-stage residual melts and hydrothermal fluids.

 

As the syenite cools, early-forming minerals such as feldspar and nepheline remove major elements, leaving Mo-enriched fluids that move along fractures, pegmatitic pockets, or other structural zones within the rock. These fluids crystallize molybdenite under low-silica, slightly reducing, sulfur-rich conditions, often alongside accessory minerals like apatite, titanite, amphibole, and sometimes corundum. The combination of the syenite’s chemistry, fracture networks, and pegmatitic zones creates ideal conditions for molybdenite to form, making it a natural product of the same nepheline syenite that hosts corundum at Craigmont.

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Why corundum is often found along a marble contact

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Corundum is commonly found near marble in places like the Craigmont Corundum Mine because those environments create the exact chemical and geological conditions needed for aluminum oxide (Al₂O₃) to crystallize without forming other minerals first.

 

The key is silica deficiency. Marble forms from limestone, which is mostly calcium carbonate and contains very little silica. When aluminum-rich fluids or melts (often derived from nearby syenitic or metamorphic rocks) interact with this silica-poor marble, there isn’t enough silica available to form common aluminum silicates like feldspar or mica. Instead, the aluminum is “forced” to crystallize as corundum. In more silica-rich rocks, corundum almost never forms because the aluminum gets locked into those silicate minerals instead.

 

There’s also a strong metamorphic and metasomatic component. In the Bancroft region, high-grade Grenville metamorphism and later fluid movement caused chemical exchange along contacts between nepheline syenite and marble. These fluids can strip silica away or introduce aluminum, further enhancing silica-undersaturated conditions. The result is that corundum tends to form right at or near the marble contacts, often alongside minerals like spinel, phlogopite, and scapolite. So, it’s not the marble itself that “contains” corundum—it’s the chemical contrast and fluid interaction at the boundary that makes those zones ideal for its formation.

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Craigmont vs Princess Sodalite Mine Geology

 

The Craigmont Corundum Mine and the Princess Sodalite Mine share very similar geology because both are hosted in alkaline, silica-poor nepheline syenite systems within the Grenville Province, where low silica and high alkali content allow unusual minerals to form—corundum at Craigmont and sodalite at the Princess Sodalite Mine. Late-stage metasomatic fluids played a major role in both areas, removing silica and redistributing elements, creating altered, patchy “hybrid” zones where mineralization is concentrated.

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Sodalite forms instead of corundum when the chemistry favors sodium over aluminum while still being silica-deficient. At Princess Sodalite Mine, highly sodium-rich, silica-poor nepheline syenite with chloride-bearing fluids stabilized sodalite rather than corundum.

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Corundum, Sapphire, and Ruby: Trace Elements and Color

 

Whether a corundum crystal appears as colorless corundum, blue sapphire, or ruby depends on the trace elements present during its formation. Iron and titanium in combination with Al2O3 produce blue sapphires, chromium produces rubies, and other impurities can give yellow, green, or pink hues. High temperatures favor crystal growth, but small differences in temperature or pressure can change which trace elements are incorporated.

 

Temperature plays a major role in how trace elements enter the crystal structure of corundum (Al₂O₃) because it controls both lattice flexibility and element mobility during growth. At higher temperatures, the crystal lattice expands slightly and becomes more tolerant of substitution, allowing larger or differently charged ions like Fe²⁺, Ti⁴⁺, Cr³⁺, and Mg²⁺ to more easily replace Al³⁺. This is why high-temperature environments (like those in nepheline syenite systems such as Craigmont) often produce corundum with more complex trace element signatures, and it would appear the colors of a multi-hued gemstone pallet.

 

In contrast, at lower temperatures, the lattice is more rigid and selective, so fewer trace elements can be incorporated, and those that do tend to be closer in size and charge to aluminum. Temperature also affects diffusion rates—higher temperatures allow elements to move more freely through melts or fluids and into growing crystals, while lower temperatures limit this process. Overall, higher temperatures generally lead to greater trace element incorporation and more chemical variability, while lower temperatures produce purer, more chemically restricted corundum.

 

Time stretched out over eons and stable environments are crucial—rough corundum is a product of an unstable environment and rapid crystalizing.

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Working Ontario Rivers for Sapphire

 

When searching for gem-quality sapphires in Ontario rivers, focus on gravel bars and sediment accumulations near or downstream of nepheline syenite outcrops. Now this is not to say that Ontario's rivers are brimming with gem sapphires, but I don't really know anyone who has looked too hard.

 

Begin the search by looking for heavy, dense crystals in riffles, since corundum sinks more readily than quartz and can concentrate in slower-moving sections of the river. Heavy minerals seldom travel too far from their source so I'd imagine that any finds would be relatively close to their source.

 

Glacial deposits and reworked sediments are also prime targets, as many Ontario sapphires have been transported and redeposited over time. Prioritize rivers draining silica-poor terrain rather than quartz-rich areas, and pay special attention to tributaries and smaller creeks connected to known nepheline syenite belts, where medium-sized blue-grey corundum crystals are often found. By combining knowledge of local geology with careful observation of river sediments, collectors can maximize their chances of finding rare gem-quality sapphires.

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Collecting Corundum in Ontario: Tips and Localities

 

Much as I appreciated the view from atop the mountain, with trees and lakes stretching off into the haze of the Ottawa Valley, I too was here to gather corundum. In perfect growing conditions, this corundum would be much like the pebbles found in Sri Lanka’s “Illium” gravels, as gemstones—sapphires or rubies. Craigmont corundums are most typically brassy and barrel-shaped, though at Princess Sodalite Mine corundum is scarce, but what there is has been found to form as flat, tabular crystals. Weathered and transported pebbles of corundum are found in glacial or nearby river sediments, often lacking crystal faces. Rarely, some Craigmont sapphires show minor star effects.

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Some better quality Ontario sapphire has been found in this area, though the odds of a world-class specimen are slim. On Lot 19 in Dungannon Township, blue and grey corundum crystals were found in diameters of up to 2 centimeters. I had visited the nearby Gutz farm in Brudenell Township, hammering brown prismatic crystals from a shallow pit. Possibly the pinnacle of Ontario sapphire comes from the banks of the York River near Egan Chutes, where blue corundum crystals up to 5 centimeters have been found, sometimes enclosed by grey material, indicative of changing conditions during formation.

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Field Guide: What to Look for in Ontario Corundum

 

What to look for in the field:

• Low quartz content (very important—corundum forms in silica-poor systems)

• Coarse feldspar + nepheline

• Muscovite “books” (often associated with corundum)

• Dark minerals like hornblende or pyroxene

• Garnet present (a good indicator you’re in the right zone)

 

Corundum at Craigmont commonly appears as:

• Stubby hexagonal crystals

• Barrel-shaped grains
  Colors: bronze, greenish, grey, sometimes dull-looking

FAQ: Finding Corundum and Sapphires in Ontario

 

1. Where can I find corundum in Ontario?
Top spots include Craigmont Corundum Mine, Egan Chutes (York River), Dungannon Township, Gutz Farm, and Burgess Mine. These areas sit on silica-poor nepheline syenite belts, ideal for corundum and sapphire crystals.

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Note: Egan Chutes is a Provincial Park so no collecting there

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2. Which rivers are best for sapphire hunting?
Look along rivers and tributaries draining nepheline syenite outcrops, especially the York River near Egan Chutes. Gravel bars, riffles, and glacial deposits often concentrate heavier corundum crystals.

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3. What does Ontario corundum look like?
Most Ontario corundum is brassy, bronze, or greenish, barrel-shaped or stubby hexagonal. Blue sapphires are rarer, often with translucent cores and grey outer zones, sometimes gem-quality.

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4. How do I spot promising rocks for corundum?
Target silica-poor, nepheline-rich rocks, especially altered zones along contacts with gneiss. Indicators include coarse feldspar, muscovite “books,” hornblende or pyroxene, and garnet. Avoid quartz-rich rocks—they rarely contain corundum.

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5. Why are some crystals blue, red, or grey?
Color depends on trace elements during formation. Blue sapphires have iron and titanium; rubies have chromium; grey or brassy corundum lacks strong coloring elements. Rock chemistry, fluids, temperature, and pressure all affect the final color.

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Corundum in Ontario is a multi-faceted Mineral

 

Finding corundum in Ontario offers a unique blend of history, geology, and adventure for rockhounds. Sites like the Craigmont Corundum Mine, Princess Sodalite Mine, Robillard Mountain, and Egan Chutes reveal how silica-poor nepheline syenite, metasomatic alteration, and trace elements combine to form corundum, sapphire, and ruby crystals. While high-quality gem specimens are rare, Ontario continues to provide rewarding opportunities for collectors to explore mineral-rich landscapes and uncover unusual corundum forms. By targeting silica-deficient rocks, altered contact zones, and hybrid syenite-gneiss interfaces, mineral enthusiasts can increase their chances of success in Ontario rockhounding, adding both knowledge and spectacular specimens to their collections.

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Note: There seems to be a lot of controversy around ownership of the mountain and so you need to check before visiting.

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Michael Gordon’s Bio

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Michael (Mick) is a longtime rockhound who specializes in the Bancroft area. He has a degree in geography from the University of Guelph, a diploma in gemology and a certification as a professional diamond grader. Michael is author of several books, the most relevant being the 3 part Rockhound Series. As curator of the YouTube channel, “caver 461” you may already have seen some of his videos. As a licensed prospector Mick is busy ferreting out great places for rockhounding – he and Mark are both co-founders of the pay to dig location Dark star Crystal Mines.

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References:

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1. Adams & Barlow (1910) – Geology of the Haliburton and Bancroft areas, Province of Ontario (Geological Survey of Canada Memoir 6): classic regional geology covering alkaline rocks including corundum‑bearing units in Ontario.

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2. Ellsworth (1932) – Rare‑element minerals of Canada (Geological Survey of Canada, Economic Geology Series 11): includes early discussion of corundum and accessory minerals in Canadian deposits.

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3. Sabina (1971) – Rocks and Minerals for the Collector, Ottawa to North Bay, Ontario (GSC Paper 70‑50): overview of mineral occurrences in Ontario including corundum.

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4. Hewitt & Carlson (1998) – Geology of the Brudenell‑Raglan area (Ontario Dept. of Mines ARV62‑05): describes the geology and stratigraphy of the Craigmont corundum‑bearing rocks.

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5. Ontario Dept. of Mines (ARV69‑08, 1961) – Nepheline syenite deposits of southern Ontario by Hewitt, Armstrong & Tilley: authoritative provincial summary of nepheline syenite geology.

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6. Johnston (1915) – A list of Canadian mineral occurrences (GSC Memoir 74): early catalogue including Klondike/Craigmont corundum and nepheline syenite locales.

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7. Satterly (1944, 1977) – Mineral Occurrences in the Renfrew Area (Ont. Dept. of Mines annual report volumes / catalogue of ROM localities): includes Craigmont and other Ontario corundum records.

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8. Tilley, Gittins & Scoon (1961) – Igneous nepheline‑bearing rocks of the Haliburton‑Bancroft province of Ontario (Journal of Petrology 2(1):38–50): detailed petrographic and petrogenetic study of nepheline syenite magmatism in the region.

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Last updated 2026