Gold in Granite: New Quartz Vein Discovery Near Melbourne

I love prospecting for gold. It’s my favourite pastime. While it’s fun to prospect in known locations, my biggest passion is finding gold where gold has never been found, or where it isn’t expected to be. And in this video, we’re going to cover my recent discovery. Gold has never been found in this part of Melbourne. It’s never even been found anywhere close to it. Whilst I won’t give the exact location away, it’s somewhere close to the CBD of Melbourne. While it’s exciting to find gold in a new location, it’s not the discovery of its existence that makes it exciting—it’s how it has been deposited.

The gold here is associated with a granitic system, which is significant because it completely differs from the typical gold deposits in the Melbourne zone that are orogenic in nature, formed from metamorphic processes during mountain building processes. Finding gold linked to a granite system suggests an entirely different mineralization process, something tied to magmatic-hydrothermal activity, where fluids expelled during the final cooling stages of the granite intrusions transported and deposited gold in the surrounding rocks and quartz veins.

This implies the presence of a hidden mineralized system beneath the surface of the CBD, something that hasn’t been explored or discovered in this area before. Now I’ve found compelling evidence of something huge beneath Melbourne. That warrants a video of its own so look out for that one soon. This article is about the significance of finding gold associated in what was once a massive magma chamber churning beneath Melbourne over 350 million years ago.

I’ll go into how gold was deposited in magmatic hydrothermal quartz in a moment because it’s key to understand what we’re seeing here, before I dive into the discovery, and my process of finding the gold. It’s a rare occurrence to find evidence of gold mineralization related to granitic batholiths in such an unexpected location. This discovery could potentially reshape our understanding of Melbourne’s geology and its mineral potential. It's not every day that you come across something that’s a literal game changer for the mineralogy of the Melbourne area.

Now volcanic gold is generally fine to microscopic in size. It isn’t associated with massive nuggets. In fact, many commercial gold mines, mine ore where gold is entirely microscopic in the rock with grades of a few grams per ton. But I did find a rock with visible gold in the specimen, which is quite rare to say the least. Gold in volcanic environments is generally fine to microscopic due to the geological processes involved in its formation. its largely due to the physical and chemical processes governing the transport and deposition of gold.

In magmatic hydrothermal systems, the fluids cool rapidly as they move away from the heat source (granite intrusion). Rapid cooling reduces the time available for gold particles to grow into larger crystals. Gold often precipitates onto pre-existing mineral surfaces (e.g., quartz, sulphides). Fine-grained or microscopic particles are more likely because they provide a high surface-area-to-volume ratio, making them energetically favourable for precipitation.

Magmatic hydrothermal systems involve complex, fractured networks where fluids move in pulses. These conditions favour dispersed precipitation over broad areas rather than the localized concentration needed for larger gold particles to form. In magmatic hydrothermal systems, steep pressure or temperature gradients are common. These changes can trigger rapid gold precipitation, but under such dynamic conditions, fine-grained particles are more likely to form than large crystals. There is always a chance for volcanic gold to be enriched by secondary processes, that occur when subduction events reconcentrate gold, but since this is a Devonian age granite, this was emplaced after the subduction events occurred in this area, so it’s never had a chance to be reconcentrated and further enriched. It’s just sat here for over 350 million years unaffected by tectonic process.

Now gold precipitates from hydrothermal fluids under two mechanisms:

One is Boiling: When fluids boil, dissolved gases escape, altering fluid chemistry and causing fine gold to precipitate.

Mixing with Cooler Water: When hot, gold-bearing fluids mix with cooler meteoric water, they lose their ability to carry dissolved gold, resulting in fine-grained precipitation.

Now since the gold is visible here, that means:

The fluids have an unusually high gold concentration

The system provided large open spaces like fractures or cavities for the gold to grow into coarser particles.

There was an ability to foster Prolonged Crystallization.

Gold deposition occurs over an extended period, allowing crystals to grow larger. Fine or microscopic gold is the norm in magmatic hydrothermal systems due to:

The Low gold concentration in fluids.

The Rapid cooling and dynamic fluid flow.

And an Association with sulphides and dispersed precipitation mechanisms.

Visible gold is less common but can occur in specific, high-grade systems or under conditions that favour extended or localized gold deposition. Since I’m observing mostly fine gold in the deposit, it aligns well with the characteristics of magmatic hydrothermal systems.

Now let’s get into the details. I found an outcrop of granite a year ago, with an inclusion of quartz veins. I’ve walked past it dozens of times, and have always said, man, I really need to grab some of this and try and crush it.

Half a year or so ago, someone jogged or rode their bike over it and dislodged a piece of it. So, I figured I’d do what I always do and bring it home to join my ridiculously large rock collection. It sat there for months, and I kept looking at it thinking I really need to crush this rock and pan it for gold.

So, this was my thinking going into it:

We have a granitic outcrop, that’s been fractured and filled with quartz at some point in time.

The granite isn’t listed on any geological maps, and it has only recently been exposed due to the dirt track that’s pounded the earth down to reveal it and because it’s resistant to erosion, the sedimentary rocks around it have worn down.

It outcrops in two areas. One is pure granite, the other includes a relatively wide quartz vein.

I’ve estimated it’s about 6 to 8 meters wide.

Because it’s granite, located in Melbourne, I suspect its age is the late Devonian. Occurring between 382.7 million years ago to 358.9 million years ago like most granite in Melbourne is. This means, in the late Devonian, magmatic hydrothermal fluids travelled through the fractures in the granite. This process happens in the late magmatic to early post-magmatic stages when the magma chamber begins to completely solidify into granite, and a little after solidification occurs. It’s a post magmatic event that has occurred here.

So, this appears to be a granite-hosted hydrothermal system based on these large feldspar crystals that appear on the quartz veins. Now I’ve already crushed most of the quartz that I got from this area, but on the video we made (link below) we show some fragments that were spared. The quartz veins themselves, are very crystalline in appearance, further pointing to a magmatic origin. Quartz in granite-associated veins tends to be more crystalline and well-formed, with larger, euhedral crystals in some cases. The quartz is often clear to milky white, but impurities can give it colours like smoky grey or even slight hues of pink (from feldspar presence) or green (from chlorite).

Quartz veins associated with granite are generally more crystalline because they form in a higher-temperature environment where crystals can grow larger and more perfectly shaped. Orogenic quartz veins, by contrast, form under faster cooling conditions and high-pressure settings, leading to a more massive and compact texture.

But let’s cut to the interesting part now. I did three separate tests. The last one I didn’t record, but prior to testing each batch, I made sure to wash my sieve, pan, the crusher, and any other tools used in the process to ensure there was no cross contamination. Each test revealed tiny specks of gold after the crushing and panning was done.

This discovery is more than just a curiosity—it challenges long-held assumptions about Melbourne’s geology and opens intriguing questions about the city’s hidden mineral wealth. Finding gold in a granitic system where none was expected is a rare and exciting revelation, one that hints at deeper, undiscovered mineralization beneath the urban landscape. Of course, its implications more so affect the geological history of Melbourne, rather than any commercial potential—since the gold occurs within the CBD and surrounding suburbs, it’s not something that could ever be mined.

While the gold here is fine, and not the large nuggets some might hope for, its presence is what truly matters. It signifies a magmatic-hydrothermal process that occurred over 350 million years ago, shaping the geology beneath Melbourne in ways previously unrecognized. This is the type of discovery that could reshape our understanding of the region’s geological history and perhaps even hint at further hidden deposits waiting to be explored.

As always, discovery is just the first step. There’s much more to investigate, and I’ll be diving even deeper into the implications of this find in a future video. So, if you’re as fascinated by the science and mystery of gold as I am, stay tuned—because this is just the beginning.

Here's the video we made on The Recent Gold Discovery in Melbourne on the OzGeology YouTube channel: