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This Internet case study is copyrighted (©) 1998 by Kevin A. Morin and Nora M. Hutt.
To participate in the International Year of the Ocean (IYO), the Minesite Drainage Assessment Group (MDAG) undertook a research program to locate old minesites located on islands. The objective was the delineation of environmental effects and environmental recovery from historical mining on relatively small and well defined ecosystems of islands. A critical criterion was that mining activity had to be at least 50 years ago.
One candidate was the island of Banaba, part of the island nation of Kiribati and northeast of the Solomon Islands in the western Pacific. Phosphate mining, which was locally heavy on some Pacific islands in the late 1800's and first half of the 1900's, displaced the local inhabitants of Banaba and eventually disrupted roughly 90% of the surface area. However, Banaba is not suitable for our research at this time, because mining ended only about 20 years ago and the story of mining impacts on Banaba is mostly socioeconomic in nature. Nevertheless, it is interesting to read about the island, its people, and mining. There is a website dedicated to it (see our Links page) as well as books like the Book of Banaba (1994, University of South Pacific Press, Fiji).
The best candidate located to date for this MDAG/IYO research project was Aruba (Map 1). Aruba is a relatively small island (52 km2) in the southern Caribbean Sea, approximately 25 km from Venezuela at 12oN latitude, and part of the Kingdom of the Netherlands. The highest elevation on the island is 188 m, and thus it is semi-arid with average annual rainfall around 0.4 m and average air temperature of +27oC.
Click on Map 1 to enlarge it.
According to oral history, gold mining in Aruba reaches back to about 1820 when a child found a large gold nugget in a dry river bed, eroded from an ore body at a higher elevation. The Aruban gold rush was on, with people digging up the dry river beds to sift for gold. During our recent visit in May of 1998, we could find no evidence of large piles or massively excavated river beds. Therefore, remnant environmental effects from this early stage are minimal.
There were two primary gold mining areas on Aruba. The first was centered near the highest point in Aruba, Jamanota (188 m, Map 1), and the second area was around to Jaburibari. These mines were Type 1 underground workings (not free draining, see Environmental Geochemistry of Minesite Drainage and the Internet Case Study for March 1998), so their surficial effects were expected to be minimal.
Gold Mining and Milling Around Jamanota
Underground mining around Jamanota (Map 1) began around 1840. Decades later in 1885, a Dutch geologist described the mine as primitive, decrepit and deserted. However, mining restarted in the area around 1901 using steam power for equipment. By 1908, 700 kg of gold had been extracted from this area. We could not locate any surficial evidence of this mining, but some structures reportedly exist.
The ore from around Jamanota was transported several kilometers to the southwest to a mill at Balashi (Map 1). This mill was built in 1899 and reportedly operated until around 1916. The ruins are still visible (Photo 1) and show that processing probably included both cyanide leaching and roasting (note concrete-lined vats in Photo 1; rusted oven not shown in photo). Below the mill, to the south, there are at least several thousand tonnes of tailings (Photo 2). The tailings are generally fine grained quartz, retain water for some time after a rainstorm, and for the most part have prevented revegetation. The tailings range in colour from light grey (perhaps windblown) to red-brown indicating significant iron oxidation (Photo 3), and there are some sulphides still present in places.
Click on Photo 1, 2, or 3 to enlarge it.
The primary environmental effects in this area of Aruba come from the tailings area. At least portions of the tailings were, and probably still are, acid generating. However, the dry climate apparently minimizes the extent of oxidation and precludes off-site migration of contaminants.
Gold Mining and Milling Around Jaburibari
The second underground mining area was close to Jaburibari (Map 1 and Photo 4). The ore from this area was transported less than a few kilometers northwest to Bushiribana on the north central coast, to a rock-walled building resembling a small castle built into a rock outcrop (Photos 5 and 6). This mill was reportedly built around 1874 and operated for 10 years. Processing apparently included both smelting, producing red-brown slag, and cyanide leaching which produced fine-grained tailings.
Click on Photo 4, 5, 6, or 7 to enlarge it.
Remnants of the slag are still visible between the smelter and the shoreline, within indentations of the surficial coral rock (Photo 7). This slag can be traced to the water's edge and thus the slag was presumably allowed to flow directly into the sea. There is also a 3-m-deep sump near the shoreline apparently with a subsurface outlet at the base (top of sump just visible in Photo 7), which would have stored and facilitated disposal of slag or tailings.
Because this part of Aruba's coast has relatively turbulent seas, the slag has been extensively eroded away, both above and no doubt below the water line. As a result, visual evidence of mine wastes after 110 years was only the minor remnant slag and tailings.
Old Gold Mines for Fun and Recreation
Some inhabitants of Aruba have found that the old underground gold and phosphate workings provide recreation through spelunking. Details of this activity can be found on the Internet at: http://visitaruba.com/setaruba/
Phosphate Mining on Aruba
There was open-pit and underground phosphate mining on Aruba, like on Banaba and Pacific islands, but we could find no details on these Aruban mines. The phosphate mines are apparently much younger than the underground gold mines, probably only a few decades old.
The Type 1 (no surface outflow) pits have not been reclaimed and thus have significant visual impacts (Photo 8). They also apparently intercept the groundwater table in places and thus represent groundwater discharge zones. As a result of the groundwater discharge, the lack of outflow, and the ongoing evaporation in the hot, dry Aruban climate, the water in these pits likely has elevated salinity. This aqueous salinity, plus elevated phosphate and perhaps elevated nitrate from any blasting, would be the primary geochemical effects, as heavy metals and acidity are not common in phosphate pits. (Note: strong acidity is common from phosphate tailings, but such tailings were not seen on Aruba and there are no reports of phosphate processing on Aruba).
Click on Photo 8 or 9 to enlarge it.
Gold mining and milling took place on the Caribbean Island of Aruba between 70 and 150 years ago. The remnant environmental effects from this historical gold mining are minimal for two primary reasons.
First, the gold mines were Type 1, so that no water could drain from them and release metals to the biosphere. Also, Type 1 mines cannot be seen readily, except by local enthusiastic cavers, so visual effects are minor. The Aruban phosphate-mine pits, on the other hand, are readily visible and thus have significant visual effects. However, they are Type 1 pits with no surficial drainage, so off-site surface effects are minimal and groundwater effects are unknown.
Second, the dry climate of Aruba minimizes migration of drainage from the mine wastes like the tailings near Balashi. This climate also suppresses reaction rates that require moisture, like sulphide oxidation. In the case of Jaburibari, the tailings and slag on the shoreline were apparently eroded over the decades, except for a few minor remaining pockets.
This MDAG research project is continuing! We are searching for other sites or case studies. Please contact us if you have a suggestion!
© 1998 Kevin A. Morin and Nora M. Hutt
For more case studies, see Environmental Geochemistry of Minesite Drainage: Practical Theory and Case Studies.
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