Tungsten Mine.
The former Needle Hill tungsten mines are among the largest mining operations Hong Kong has ever seen. There are large tunnel networks dug out in the hillside, this cache showcases two of the adits. The listed coordinates are the entrance of Adit 31A, where a single vein was mined. The coordinates of the second stage are the entrance of Adit 8, where an ore (most likely galena, a lead ore) is visible. The order you visit these two adits does not matter.
You have to enter the mine; so bring a strong flashlight. Wear good shoes and clothes that can handle a little dirt, wearing a hard hat (safety helmet) is a must when entering these tunnels.
Be aware of the high terrain rating. Adit 31A is the hardest to reach, as it requires climbing up a slope covered in loose rocks. Adit 8 is a bit easier to get to (along a T3-level trail) but the entrance is partly blocked off and the first part of the tunnel is flooded, the water is about ankle deep. Waterproof hiking boots should be able to keep your feet dry.
A short history of tungsten mining at Needle Hill.
Wolframite deposits were discovered in 1935, and a mining licence issued in the same year. Mine development commenced in 1938 and continued throughout the Japanese occupation. Mining activity, including unlicensed surface excavations, increased during the Korean War period of 1949-1951 when tungsten prices rose sharply. Over its 29 years of production, the mine yielded 1,000 tons of wolframite concentrate. A peak output of 12 tonnes per month was achieved. By 1967, declining tungsten prices and increasing labour costs prompted the suspension of mining operations.
Around 1950, at the peak of production, some 5,000 people worked in the mines, many of which were unlicensed. These unlicensed mines left serious scars in the landscape, many of which are still visible today.
The mines were abandoned, and the entrances to some closed off, though this was not done very properly and many are still accessible, however some are flooded. Lower mines were lost to the development of the Shing Mun reservoir. The existing mine shafts have not been maintained since the mines closed, some have caved in, others are filled with water or mud.
A more detailed discussion of the history of the mines, including geological maps of the area can be found in this newsletter from the Geological Society of Hong Kong, pages 29 to 40. This also includes a map showing locations of other mine entrances, and a map of the rather extensive tunnel network behind adit 3 and adit 8.
Geology of the area.
The main rocks in this area belong to the Needle Hill Granite formation, a mostly light grey coloured, fine to medium grained monzogranite. This granite bedrock contains quartz veins, which were formed by intrusion of mineral rich liquids along faults and cracks of the southern slopes of Needle Hill.
The veins that have been mined have a typical thickness of 30-40 cm, and extend for up to a couple hundred meters in both horizontal and vertical directions. A more detailed discussion on the formation of quartz veins can be found here, a little down on the same page the formation of ore veins is discussed.
Tungsten deposits.
Tungsten occurs naturally in various forms, in the case of the Needle Hill mines the deposits are in the form of the black mineral wolframite, which was found along quartz veins in concentrations of about 0.33%. Wolfram is another name for tungsten. Besides tungsten, some mineralisation of molybdenum has taken place here as well, however this metal has never been mined commercially here, not even as by product of the tungsten.
As the tungsten was found along quartz veins, this meant a large quantity of granite and quartz had to be excavated to get to he wolframite. This waste was often dumped simply on the hillside below the mine entrance, these debris piles are still visible today.
Adit 31A.
One part of this cache is in one of the smaller adits: 31A, a single tunnel to get to a quartz vein. Under this entrance there is a large debris pile consisting mainly of milky white chunks of quartz, be very careful when climbing up these loose rocks to the mine entrance. There are established routes over the debris from the main path up to the adit.
Enter the tunnel, and after about 20-30m there is a deep, narrow trench that extends in all directions: this is where the wolframite was mined. Be careful not to fall into this trench, it is really deep. The tunnel continues for a bit after this trench. Geological maps indicate a second parallel mineral vein nearby, but no traces of it are visible in the tunnel extension. Old, mostly rotten wooden supports can still be seen which may have been used by the miners to build scaffolding.
The tunnel is narrow, just enough for a person to pass through. Mined ore was carried out by hand, maybe using a wheelbarrow. The vein it leads to is almost perpendicular to the tunnel in both horizontal and vertical direction, as only the quartz with minimal surrounding rock has been excavated the shape of such a vein inside the bedrock is showcased here.
Where the tunnel crosses the vein, a bit of the original vein is still in place forming a kind of bridge. Also at the edges of the mined area you can see the quartz vein. This vein is clearly narrower than the excavated space, as extra quarrying had to be done to give sufficient space for the miners to work in.
Question for Adit 31A.
The vein you see here - as in, the open space where the vein used to be - looks a bit like a sheet, with a thickness of 30-40 cm, wedged in the rock. How did the quartz end up being shaped like that?
Adit 8.
The other half of this earth cache is inside Adit 8. From adit 31A follow the miner's trail in eastern direction to waypoint DOWN, from where you turn right and take the trail down to waypoint ADIT8.
This is one of the larger adits of the mine operation, forming a large tunnel network with adit 3. As there are multiple entrances to this network there is good natural ventilation, you can feel the wind at the entrance. Traces of electricity supply, broken light bulbs and remains of a mine railway can still be seen in the tunnels. The tunnel is wider and taller than Adit 31A, probably to have enough space for the railway cars. There are several higher and lower levels, beware to not fall into one of the lower levels as there are no fences around the holes. The lower levels are flooded, and as such inaccessible.
To get to the cache, enter the tunnel, and take the second tunnel to the left, marked "A VEIN NORTH". Walk along the remains of an ore chute, then over a pile of debris, and another 8m onwards look at the roof. The ore bearing white quartz vein is clearly visible in the roof. At the cache location you see a metallic shiny mineral in the quartz, this is the ore. All the quartz and the rock around it was just waste. The ore you see here is most likely not wolframite, the material that was mined here. Wolframite is black, while this ore is metallic in colour. Also such an obvious occurrence of wolframite would certainly have been mined already. This ore is very likely galena a lead ore that is found often with wolframite. This identification is based on the fact that it is a likely mineral to be found here, and all the properties and characteristics of my sample match the description from wikipedia.
Many minerals, not only tungsten, are found along veins. The intruding liquid may contain various elements, which separate in a process called fractional crystallisation, concentrating the mineral. If such concentrations are large enough it becomes worthwhile to mine.
On the ground you can find small nuggets of the metallic ore, try to find a larger piece (1/2 cm or so, they don't come bigger). You can feel the weight of this material is much different than that of a similar sized piece of quartz or granite.
Look along the quartz vein, it is mostly white in colour but a little bit back in the tunnel there is a greenish patch in the quartz as well.
Questions for Adit 8.
- Explain the basic principle of how fractional crystallisation caused the wolframite to separate from the rest of the quartz.
- Feel the weight of an ore nugget. Is it heavier or lighter than the quartz? Why would this be?
- Normally quartz is milky white or almost colourless. What could cause part of this vein to take a green colour?
Getting there.
Take minibus 82 from Tsuen Wan to the Pineapple Dam, from there walk along MacLehose trail (section 7) to waypoint WEST, the start of an old miner's trail. At the start of that trail you may find some ruins of miner's quarters, and there are several more adits along this trail.
By car or taxi you can get to the main dam, from there it is about 15 minutes walk to Adit 31A.
Alternatively you may take a bus to Lei Muk Shue Estate and walk up to the Shing Mun Reservoir and continue on the MacLehose Trail.
Another route is to take a train to Tai Wai station, from there a taxi up Lower Shing Mun Road to the dam (see waypoint TAXI), from where it is about 45-minute walk via waypoint EAST.
All the trails you need to follow are mapped on OpenStreetMap. The trails on Google Maps are inaccurate.
Safety first!
This section is not to spoil your fun, on the contrary. Taking some precautions go a long way to prevent injury or worse, and now that would spoil the fun badly. Mines are a dangerous place, abandoned mines maybe even more so.
Make sure you are an experienced hiker and climber, some scrambling is to be done. Know your ability, do not push yourself to do "just one more" when you're tired and it's running late - just come back another time.
Wear appropriate clothes. Wear long pants to protect your knees when crawling through a small entrance. Wear a hard hat to protect your head - the tunnels are quite low, and have some pointy rocks sticking out from the ceiling that are really easy to miss. Consider wearing gloves to protect your hands.
Bring a powerful torch, preferably with fresh batteries. Bring a second torch in case the first one breaks down, so at least you don't have to feel your way out.
Do not go in bad weather. Flash floods in those mines are unlikely, but if the water level suddenly rises there is nowhere for you to go.
To log this cache.
Please e-mail me the answers to the questions above, by private e-mail (follow the link to my profile above). Do not post these answers in the logs! Photos of your adventure are highly appreciated though not a requirement.