FMF - Friends of Minerals Forum, discussion and message board

[silvia]

A brief introduction to The Rio Site at Cabeco do Piao

The Rio site contains the old mill, and a large coarse waste dump. Situated on top of the waste dump is a dried up tailings pond varying in depth from 25 to 70 metres. The dump contains coarse waste rock with minor amounts of pyrite and arsenopyrite, fine grained mill tailings, and a pile of arsenopyrite flotation tails. Estimates indicate that the total weight of the pile at Rio exceeds 8 million tonnes of material.

Until, March 21, 2006 Beralt (Tin and Tungsten Ltd) was legally responsible for the Rio site. On March 21, 2006, the Portuguese government signed an agreement that removed the site, and all associated environmental liabilities from the Beralt mining concession.

In 1904, a mechanized Mill was built in Cabeço do Pião, and historical records indicate that the disposal of mine waste at the Rio site started sometime between 1905 and 1910, and finished in 1996. In 1998 all milling operations ceased at the Rio site.

The original Mill at Cabeco do Piao was situated on a terraced slope on the left bank of the river Zezere some five kilometres west of the main mine at Barroca Grande. In 1912, an aerial cable (5100 m) was installed between Barroca Grande and Cabeco do Piao. For many years, the Rio Mill was supplied with hand-picked ore from the hand-picking plant at Barroca Grande via a rope way. In the early years of operation, cheap labour made it profitable to separate good ore from waste rock, and the only skills a good worker needed were physical strength, good eyesight and fast reflexes. Improvements in mechanization made the hand-picking plant redundant.

The Rio mill contained a Crushing and Grinding plant, a Gravity Treatment plant, a Flotation plant and an Electromagnetic Separation plant. The plant also contained well-equipped Mechanical and Electrical Workshops for the day-to-day maintenance of the plant.

Though the mill received power from a commercial power station some twenty kilometres away, it was also equipped with its own diesel-electric plant capable of supplying 1200 KVA output to meet all emergency needs at the mill.

FUTURE

There is an ongoing effort to use the waste rock to produce road construction materials.

There is also ongoing interest to turn the old facility at Rio into a tourist attraction. Some of the now abandoned facilities at the Rio site will be rebuilt to establish an interpretive mining Museum.

[silvia]

Glassy partly gemmy green color zoned tabular crystals of Fluorapatite to 2 cm in size with crystallized Quartz and Arsenopyrite.

The Fluorapatite crystals display bright orange fluorescence in the presence of UVA light.

[silvia]

Lustrous slightly translucent crystals of Cassiterite to 10 mm on a matrix composed of Muscovite, Pyrite, Marcasite and Quartz.

[silvia]

Crystals of Siderite to 3 cm in size across the top of a matrix composed of Arsenopyrite and Pyrite. Minor Arsenopyrite and pyrite present.

[silvia]

Golden crystals of Marcasite to 2 cm in size in a cluster with crystallized Muscovite, Quartz, Arsenopyrite, and Dolomite.

[silvia]

Cluster of satiny lustrous translucent prismatic Fluorapatite crystals measuring to 3 cm in size with micro crystallized Topaz, Muscovite and Goyazite. Topaz and Goyazite verified by SEM and XRD.

The Fluorapatite crystals display a ‘mild’ orange fluorescence in the presence of UVA light – not as strong as the fluorescence exhibited by the green crystals of Fluorapatite.

[Jordi Fabre]

[silvia]

Hello Jordi:

The specimen came with a label that stated Goyazite. I have no reason to doubt the analysis, but I am more than happy to organize another SEM/XRD analysis to be positively sure. My partner will look at it under the microscope in the meantime.

[silvia]

More about Panasqueira

In 1886 the first prospecting licence at Panasqueira was granted, and the first reference to wolframite occurred in 1888. In 1896 a mining company was formed to exploit the deposit. Underground mining operations at Panasqueira have been continuous since 1896, except for a brief period at the end of World War II and a second closure in the mid-1990s.

From 1937 to 2018 a total of 42 million tonnes of rock have been extracted from the Panasqueira ore-body. This rock has produced approximately 132,000 tonnes of tungsten concentrate, 7,100 tonnes of tin concentrate and 34,000 tonnes of copper concentrate.

Despite 100 years of near continuous mining, very little primary exploration has been done outside the active or past mine workings.
Several anomalous areas of elevated tungsten and tin geochemistry were established by a regional stream sediment geochemical survey carried out between from 1982 to 1984 by Beralt. However a “true” exploration of the concession and the area immediately surrounding the concession seems to have been fairly limited.

It is worth noting that the hills surrounding the mine contain many old pits and shafts left from the days of past hand mining operations.

[silvia]

The specimen comprises a cluster of gemmy Fluorapatite crystals measuring to 3 cm in width, along with minor Siderite, Arsenopyrite, and Muscovite.

[silvia]

Sharp pseudo-hexagonal crystals of Pyrrhotite to 6 cm in size with lustrous black complex Sphalerite crystals to 4 cm. Minor Quartz present as well.

[silvia]

The specimen contains incredibly lustrous sharp black crystals of Cassiterite to 35 mm in size across the front of this matrix with minor Quartz.

[silvia]

Photographing Minerals – A Tale of Frustration

I thought it would be nice to share some of my adventures with the digital camera. I am not a professional photographer – just barely an amateur one, but I have managed to take some nice photos of some of my minerals.

Polite and constructive criticisms welcome.

Camera

The camera I have used is a Nikon Coolpix A100. It has a 20.1 megapixels sensor, a wide zoom of 5X and a dynamic fine zoom of 10X. Note that I never use the zoom feature when photographing minerals. It has a LCD screen 55 mm long and 42 mm wide. When photographing minerals, this LCD becomes my defacto eye. I never look at the mineral, rather I use the LCD display to show me what the camera sees. If the mineral looks good in the LCD, the camera will take a nice shot. The camera is attached to an appropriate tripod.

Light Box

For most minerals I use a light box made of bright white plastic. It has an LED illuminator that runs off a 5VDC power supply. It is approximately 30 cm x 30 cm x 30 cm in size with a circular detachable top lid. When photographing minerals I flood this light box with light from three to four 240V globes. When the specimen is too large to fit in the box or the box does not give a good photo I will use my computer desk with the appropriate background – white or black cotton sheet.

Light Source

I use 240V/50Hz, 12W E27 globes that emit light described as ‘daylight’ (5500K to 6500K) by the supplier. Each globe is mounted in a lamp fitting that clips to the top of my computer desk.

When using the lamps all exterior light is excluded. The room is dark, and the only light comes from the lamps.

Software

Any photo editing software package can be used, such as Photoshop, Luminar AI, Adobe light room, Aurora HDR and many others. I often use a very early edition of Adobe Photoshop, circa 2010.

Miscellaneous

This includes all and anything I use to get a good photo – blocks of wood, plastic, metal or rubber to support the specimen. Sheets of folded aluminium foil to reflect light and white plastic from discarded milk containers to diffuse the light.

An example

Pyrite, Marcasite and Pyrrhotite are annoying to photograph. You can often get a very nice photograph with every aspect of the mineral in focus, but it lacks the tones that the eye sees in the specimen. I often ask where are the beautiful yellow tones of Pyrite and the bronze velvet tones of Pyrrhotite that I can see in the specimen.

I decided to use the photograph of the specimen of Sphalerite with Pyrrhotite from Dal'negorsk, Russia as an example. I had no success using my light box to photograph the specimen. Many of the photographs taken were in focus with great depth of field but they looked nothing like the specimen I had in my cabinet. So I set up my computer desk to take the photo. I used a white cotton sheet for the background, and I positioned the lights until what I saw in the LCD was what I wanted to photograph.

I used the automatic focus feature of the camera. This places a green box around that part of the subject the camera deems to be in focus. When almost in focus you get a yellow box, and when not in focus a small red box appears in the camera’s LCD.
Sometimes only part of the mineral was in focus, so I made small adjustments to the position of the lights, the location of the camera and the position of any reflectors or diffusers used to take the photograph, until the whole specimen was within the green focus box. And then I took the photograph, and continued with the process until I was happy with all the photographs taken.

Detail of Camera settings.

1. Camera is a CoolPix A100
2. Specimen 15 cm from camera lens
3. Image Mode 20w – 5152 x 3864 pixel resolution
4. White Balance set to auto
5. Continuous mode set to Single
6. ISO sensitivity set to Auto
7. AF area mode set to Target finding AF
8. Autofocus mode set to AF-F Full-time AF
9. Macro mode on
10. Flash set to off
11. Scene set to Auto mode

[silvia]

A large cabinet specimen with a ‘ball’ of Calcite 16 cm in diameter set on a crystallized Quartz matrix containing gemmy Quartz crystals covered in Calcite.

[silvia]

A cabinet size example with sparkling metallic crystals of Chalcostibite to 0.5 cm in size forming clusters to 2 centimetres across on a crystallized quartz matrix with minor Tetrahedrite.