Raymond’s Geology Blog
July 20, 2026

Geology and Mineral Resources – São Tomé and Príncipe

Introduction

Figure 1 - São Tomé and Príncipe
Credit: Mapsland, Creative Commons Attribution-Share Alike 3.0 Licence

A former Portuguese colony, the Democratic Republic of São Tomé and Príncipe is a country of 220,372 people in the Gulf of Guinea. The country has an total area of 964 square kilometres and consists of two main islands, São Tomé and Príncipe, plus associated smaller islands.

São Tomé & Príncipe is a relatively poor country with a per capita GDP (PPP) of $3,167 and a medium Human Development Index of 0.637. The local economy is based upon cash-crop or plantation agriculture together with subsistence agriculture and fishing. The cash-crop plantations cover about 90% of the available arable land and are used mostly to produce cacao for chocolate, copra (dried coconut), palm kernels, and coffee. Consequently, São Tomé & Príncipe imports food, since local production is inadequate to meet their needs. In 2024, the top exports of São Tomé & Príncipe were cocoa beans, palm oil, crude petroleum, scrap vessels, and motor vehicle parts and accessories. The top destinations were Pakistan, Netherlands, France, Poland, and Germany. In 2024, the top imports of São Tomé & Príncipe were refined petroleum, passenger and cargo ships, rice, wine, and poultry meat. The top origins were Portugal, China, Angola, Japan, and Turkey. For more details on São Tomé & Príncipe, check out the Wikipedia article on the country.

Geology

Figure 2 – Cameroon Line
Credit: Figure 1 in Tefogoum et al. 2019

The islands of São Tomé & Príncipe sit on a tectonic feature generally called the Cameroon Volcanic Line. The Cameroon Line is a series of volcanoes that stretches from Lake Chad, in the northeast, to Annobon Island, in the southwest. The formation of the Cameroon Line has attracted the attention of a lot of researchers (see here, here, here, here, and here) but seems to be related to the movement of the African Plate over some kind of tectonic “hotspot”. In the case of São Tomé & Príncipe, this resulted in shield volcanism that in turn lead to the formation of Principe island, beginning around 30.4 million years ago (Mya) during the Oligocene; and the formation of São Tomé, beginning around 13 Mya, during the Miocene.

Figure 3 – Geology of Principe
Credit: Figure 1 in Neto & Henriques, 2025a,
Creative Commons Attribution 4.0 International License

The geology of Principe island consists of two main series of volcanic series:

  1. An older series, deposited 24 Mya to 30.4 Mya, consisting of alkaline basalt and trachybasalt (hawaiite).

  2. A younger series, deposited 3.5 to 6.9 Mya, consisting of phonolitic lavas including nephelinite and basanite.

Other geologic features include Holocene aged beach deposits and crude oil seeps.

Figure 4 – Geology of São Tomé
Credit: Figure 1 in Neto & Henriques, 2025b,
Creative Commons Attribution 4.0 International License

The main features in the geology of São Tomé include:

  1. The trachytes of the Mizambú volcanic complex, 6 to 8 Mya;

  2. Chimney rocks made of phonolite;

  3. The basalt and trachyphonolite lavas of the Ribeira Afonso volcanic complex, 2.5 to 5 Ma;

  4. Basalt and trachyphonolite lavas of the São Tomé volcanic complex, less than 1 Mya;

  5. Trachyte domes;

  6. The cross-bedded sandstone sequences of the Lagoa Azul formation;

  7. Pyroclastic cones and lava fields (< 0.4 Mya); and

  8. Alluvial fans and flood deposits

The two best sources on the geology of São Tomé & Príncipe are from the same authors and were published last year:

Mineral Resources

Figure 5 – Exploration Blocks, São Tomé & Príncipe
Credit: ERHC Energy

According to the USGS, there is very little documented mineral industry in São Tomé & Príncipe. There is probably use of local rock resources for building materials, but there are no public records of this. There is, however, activity in offshore petroleum exploration. The main actors here are the Brazilian company Petrobras, with this recent press release together with Galp and Shell.

Summary

Figure 6 - Rolas Furnas Geyser
Credit: Tomek, public domain

So, there is not much to the islands of São Tomé & Príncipe. The place looks like an interesting place to visit and there is certainly lot of interesting volcanic geology. The main opportunity for geoscientists is in the offshore oil exploration. It remains to be seen what will be found and what benefit the local population will receive from the development.

Standard Caveat

J. Robert Oppenheimer on freedom and scientific inquiry

The purpose of my weblog postings is to spark people's curiosity in geology. Don't entirely believe me until you've done your own research and checked the evidence. If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here. If you want to, go out into the field and examine some rocks on your own with the help of a good field guide. Follow the evidence and make up your own mind.

In science, the only authority is the evidence.