6613615d-f02a-4cb2-ab9e-3722f96ce36e

Geoconservation Research

Geoconservation in Latin America and the Caribbean

2023, Volume 6 / Issue 2 / pages(308-321)

Amethyst Deposits of the Los Catalanes Gemological District (Artigas Department): The First Uruguayan IUGS Geological Heritage Site

1 Instituto de Ciencias Geológicas de la Facultad de Ciencias, Universidad de la República, Uruguay. 2

Dirección Nacional de Minería y Geología, Ministerio de Industria Minería y Energía. Uruguay.

Corresponding Author:

Mauricio Faraone Instituto de Ciencias Geológicas de la Facultad de Ciencias, Universidad

The recognition and valorization of geological heritage in Uruguay is an incipient and developing process. The International Union of Geological Sciences designated the deposits of amethysts of Los Catalanes Gemological District, in northern Uru- guay, as one of the first 100 “Geological Heritage Sites” on October 22, 2022, in the Mineralogy category, the first in Uruguay. It is part of one of the most important continental flood volcanism episodes on Earth (end of Jurassic to Early Cretaceous). The Paraná igneous province, a dominant tholeiitic basaltic and scarce acidic prov- ince that extends into parts of Brazil, Paraguay, Argentina and Uruguay, contains amethyst and agate deposits of unique international significance because of frequent mega-geode concentration, enormous reserves, and gemstone quality of varied size and forms. Although quartz-filled geodic cavities are common in the southern Serra Geral Formation in Brazil (Ametista do Sul, Quaraí), the more intense purple ame- thysts in giant geode deposits are found in the Arapey Formation in the lower-middle basin of the Catalán Grande stream in Uruguay. This contributes to the empower- ment and pride of the local population as well as raising awareness of the need for the conservation of part of this mineral resource. Further, there was a recent inventory assessment that contributed to the understanding of the real scientific value of this designation.

Keywords: Geological heritage, Inventory assessment, Paraná igneous province, Amethysts, Uruguay.

Introduction

Since the Romans, and from its Latin root, the term patrimonium (heritage) has contained the no- tion of father and homeland, and with this duality, it has crossed many centuries. Heritage is what we inherited from our parents and ancestors and at the same time is everything that belongs to all of us, as a community (Goso et al 2016). Under this approach, heritage is made up of objects or non-material assets.

Cultural heritage can be defined as a construction that changes according to new criteria, purposes or circumstances of each social context and with diverse meanings, which vary according to the communities (Prats 2004). This social construc- tion links interpretation, selection, historical and risk awareness about what is identified as heri- tage, and the community. The main changes in the evolution of heritage knowledge refer to the recognition, scale, spaces and plurality of repre- sentations, as well as to its use and conservation, within the framework of sustainability and citi- zen participation (Ariño 2009). This conceptual shift is reflected in the contents of agreements, recommendations and documents agreed by in- ternational organizations (e.g., UNESCO, ICO- MOS, IUCN, ICCROM). An important milestone in terms of heritage conservation was the signing in 1972 of the World Heritage Convention, which created World Heritage Sites with the main objec- tives of nature conservation and the preservation of cultural assets.

As Wimbledon (1996) states, geologists have long been concerned with the apparent imbalance of natural features in the World Heritage list, and there has been a perception that globally signifi- cant geological sites, some of them defining out- standing stages in the organic and inorganic evo- lution of the Earth, have been overlooked. It is for this reason that an indicative list (GILGES, Global Indicative List of Geological Sites) was compiled

in 1991, as a first attempt at an inventory to aid judgments on the selection of World Heritage sites, under the guidance of the International Geo- logical Correlation Programme (IGCP), the Inter- national Union of Geological Sciences (IUGS) and the International Union for Conservation of Nature (IUCN).

In past decades, the conservation of geological heritage was based on the idea that certain geo- logical features have an exceptional value in their own right and should therefore be protected and conserved. Therefore, outcrops or landscapes that present unique characteristics, either because of their singularity or their usefulness for establish- ing correlations, are fundamental for the scientific advancement and dissemination of geology (Car- cavilla et al. 2007).

In the 1990s, the IUGS Global Geosites Working Group initiated the development of a database of geological sites of international relevance through the project “GEOSITES: A global comparative site inventory to enable prioritization for conser- vation” (Wimbledon et al. 2000). The project was supported by ProGEO, created in 1993 by the Eu- ropean Association for Conservation of Geologi- cal Heritage, until 2021, as well as by IUCN and UNESCO, but did not achieve the global accep- tance initially expected the lack of widely accept- ed methodologies.

In recent years, there has been a growing inter- est in researching methods for geological heritage assessment around the world. For instance, Pro- GEO at the European level, and the Association of Iberoamerican Geological and Mining Surveys (ASGMI) in Latin America have proposed simi- lar methodologies for the evaluation of geological heritage sites (ASGMI 2018). A method based on systematic survey and assessment was developed through the GEOSITES project and applied in sev- eral European countries (Wimbledon et al. 2000).

The IUGS-ICG defined a series of main standard conditions: name of the geological heritage site;

location; geological period of the main geological interest; typology (history of geosciences, stratig- raphy and sedimentology, paleontology, igneous and metamorphic geology, volcanology, tectonics, mineralogy, geomorphology and active geological processes, and impact structures and extraterrestri- al rocks); main arguments for the designation; and scientific research and tradition (https://iugs-geo- heritage.org/subcomission-on-sites/).

According to the IUGS-ICG the main objec- tives are to:

The first objective of the IGCP – 731 IUGS GEO- LOGICAL HERITAGE SITES (IUGS – UNE-

SCO) was the creation of proper conditions of collaboration of more than 200 specialists from almost 40 nations and 10 international organiza- tions, representing different disciplines of Earth Sciences, and promoting broad participation in the selection of the first 100 geosites. During the re- quest, 181 candidate sites from 56 countries were proposed and evaluated by international experts from 34 countries. The result of this challenging and collaborative process is the list of the First 100 IUGS Geological Heritage Sites, distributed by regions: 34 in America, 28 in Europe, 23 in Asia-Pacific and the Middle East and 15 in Africa. In October 2022, during an official event in Zu- maya (Basque Coast UNESCO Global Geopark) celebrating the 60th IUGS anniversary, was the public presentation of the first 100 IUGS Geolog- ical Heritage Sites, including the first Uruguayan

IUGS Geological Heritage Site (Goso & Faraone 2022), the Los Catalanes Gemological District

represented by the abandoned Oliveira mine Geo- site in Artigas Department (Fig. 1).

Figure 1. Localization map of Los Catalanes Geomological District and the Oliveira mine Geosite.

The First Uruguayan IUGS Geological Heri- tage Site

Geological Setting

In South America, the Paraná Magmatic Province (PMP; Peate 1997), with calculated lava volumes of approximately 1.0 × 106 km3, infills and covers

1.2 × 106 km2 over southern Brazil, eastern Par- aguay, northern Argentina, and northwestern Uru- guay (Melfi et al 1988, Fig. 2).

In Uruguay, the so-called North Basin is part of the Paraná Basin, an extensive Gondwanan basin

that in Uruguay occupies about 100,000 km2 and contains in deep sectors more than 2,500 m thick- ness of sedimentary and volcanic rock succession (Ubilla et al. 2004). This thick sequence was de- posited under different structural styles from the Devonian to the Upper Cretaceous, forming a suc- cession of genetically related strata bounded at the base and top by regional unconformities (de Santa Ana et al. 2006).

Deposits of Amethysts of Los Catalanes Gem- ological District

Uruguay is a small country in South America; with 176,215 km2 of continental territory, it owns a very diverse geology. Its geological records date from the Archean to the Phanerozoic, showing nu- merous geological processes of Earth´s evolution. Recently, under the influence of the Grutas del Palacio UNESCO Global Geopark (GdPUGGp), the University of the Republic and initiatives with the support of the National Geological Survey (DINAMIGE), some studies of Uruguay’s geo- logical heritage have been published (Goso et al. 2016; Picchi et al. 2018; Goso 2021; Goso & Far- aone 2022; Martínez & Goso 2022). Taking ac- count of examples of inventories from Spain, Por- tugal, Brazil, and Argentina, in addition to criteria proposed by ProGEO and IUGS, some inventories have been carried out following the methodology of Brilha (2016) and García-Cortés et al. (2014).

In this contribution, we present the first Uruguay- an Global Geosite, Los Catalanes Gemological District (DGLC), adopted in 2022 and represent- ed by an abandoned amethyst mine. Probably this IUGS-UNESCO designation will encourage more specialists in Uruguay to submit nominations, where the heritage value of sites can be inspired by the case argued for the first global geosite of the country. The Oliveira mine is located in north- ern Uruguay (Artigas department), about 600 km from the city of Montevideo, close to a small vil- lage named La Bolsa. The relief in the area has

the typical features of a basaltic plateau, with an altitude of about 200 m above the mean sea level. Since 2016 it has been visited yearly by several hundreds of primary, secondary and university students as well as other visitors, totalling 9000 visitors per year.

Deposits of Amethysts: Historical Mining Re- view

Figure 2. Details views of amethysts geodes and mega geodes of Los Catalanes Gemological District. Photos: Mateo Acosta (Mining Safari)

The Upper Jurassic-Early Cretaceous Sequence in particular is marked by reactivation of the cratonic basement in response to the development of a re- gional extensional stress field from the slow rate of convergence between the Pacific plate and the west- ern edge of Gondwana (de Santa Ana & Veroslavsky 2004). The association of Mesozoic magmatism with tectonic events responsible for the opening of the South Atlantic Ocean is well represented on the South American platform. These tectonomagmatic processes were precursors of the geological transfor- mations related to the continental break-up and the oceanic expansion (Tankard et al 1996). The tholeiit- ic or alkaline magmatic manifestations associated with this tectonic event belong to the Paraná-Etend- eka Province, comprising the South American and African remnants (Peate 1997, Fig. 3).

Figure 3. Localization map of the Paraná Magmatic Province. Modified of Muzio et al. (2022).

Uruguay presents a bimodal volcanism Mesozoic record, part of the Paraná Igneous Province (lo- cally, Arapey Formation), the northeast with basic magmatism and in the southeast with acid extru- sive rocks. Rapid eruption rates (i.e., over a few million years) according to Renne et al (1992) and Peate (1997) reflect adiabatic decompression melting in the convecting mantle whereas a much longer duration of igneous activity (perhaps over 10s million years) is associated with alkaline vol- canism.

The Arapey Formation, almost 40,000 km2 in extent (Fig. 4), is mainly composed of medium- to fine-grained basaltic rocks of tholeiitic nature (Muzio 2004). These lava flows (Russo et al. 1979) are up to 1050 m thick, and correlate with the Alto Paraná Formation in Paraguay (450 m maximum thickness), Serra Geral Formation in Brazil (1700 m thick), and the Posadas Member of the Curuzú Cuatiá Formation in Argentina (185 m thick).

Figure 4. Geological map of northern Uruguay showing Arapey Formation distribution (green color). Based on Preciozzi et al (1985).

During the first phase of a geological survey of amethyst and agate occurrences in the northern Artigas Department conducted by DINAMIGE (Fig. 5), Techera et al. (2007) defined LCGD as an area of about 500 km2 located 50 km SE from Artigas city. These authors identified six spill ba- saltic flows about 200 m thick in total in that area, three of them rich in mineralized geodes (numbers 2, 3 and 4). Intercalating aeolian sandstones each 7 to 14 m thick were described between number 3 and 4 spills (Fig. 5).

Duarte et al. (2009) described both the Los Cat- alanes and Ametista do Sul districts as thinner (10–30 m) spill lavas (type I; Gomes 1996) with a massive internal portion containing a geode-bear- ing mineralized zone (Fig. 6). Thicker (30–60 m) layer lavas (type II; Gomes 1996) display vertical joints of colonnade and entablature types (Fig. 7). Upper and lower vesicular zones are present in both types I and II.

Figure 5. Geological map of the LCGD and localization of the Oliveira mine. Source: Techera et al (2007)

Figure 6. Internal structure sketch of basaltic mineralized flows in LCGD. Modified from Techera et al (2007)

Figure 7. The internal structure of lava flows from the mining districts. A) Type I described by Gomes (1996); B) Type II, also named by Gomes (1996) and previous description by Long and Wood (1986).

Morteani et al. (2010) proposed that these mineral deposits were formed as protogeodes by bubbles of CO2-rich basalt-derived fluids. The formation of the celadonite rim and the

lining of the geodes by agate followed by quartz and amethyst were driven by the artesian water of the Guaraní aquifer percolating the basalts from below. The temperatures of the amethyst forma- tion were estimated from fluid inclusion data to be between 50° and 120°C.

In a regional study of the Arapey Formation, Waic- hel et al. (2010) identified three types of extrusive patterns: pahoehoe, ‘a’a and massive. According to these authors, the predominance of pahoehoe flows at the base of the sequence in Uruguay in- dicates a low eruption rate established on soft paleosurfaces that must have facilitated the dis- placement of lava generating volcanic successions with great lateral extension. The overlapping ‘a’a effusions indicate an increase in the eruption rate and/or paleosurfaces with a steeper slope. Artigas geodes occur associated with thin ‘a’a flows.

Duarte et al (2011) proposed for the gemological district that two flows are mineralized, a basalt and a basaltic andesite (both low-Ti, Gramado type). Fluid inclusions, alteration mineralogy, and oxy- gen isotopes indicate the involvement of low-tem- perature fluids of meteoric origin in the formation of the geode fillings. Low sulfur isotope values on altered basaltic host rocks, down to -15%, indicate the involvement of sedimentary sulfur affected by bacterial sulfate reduction.

Da Silva (2011) reports the discovery of many gossans in the intraplate Paraná volcanic province, based on observations of satellite images and field work associated with rock geochemistry and geo- physics. The study area is located on the border between Brazil and Uruguay and covers the min- ing district of Quaraí and the gemological district of Los Catalanes. Gossans also indicate a straight-

Arduin et al. (2022) proposed three stages in the filling of the geodes based on mineralogy and flu- id inclusion analysis. The first stage includes ce- ladonite, zeolite, chalcedony, calcite, microcrys- talline quartz, pyrite and chalcopyrite, the second macro-crystalline colorless quartz and amethyst, and the third stage late calcite and sporadic fluo- rite. The authors proposed an interaction between the lava flows and meteoric water.

Regarding the study of these mineral resources, Techera (2011) presents a mining report with spe- cial references to the gemstone quality properties of these deposits and economic data about export and main countries’ sales. The main markets for these gemstones are Germany, the United States of America, Brazil, and China, with exports reaching annually several million dollars.

Deposits of Amethyst Inventory Assessment

The inventory and quantitative assessment of geo- logical heritage, the most valuable occurrences of geodiversity, are essential steps in any geoconser- vation strategy and the establishment of priorities in geosite management (Brilha 2016). Despite the existence of many geological heritage invento- ries at different scales, the inventory assessment proposed by Brilha (2016) was applied by Salles (2023) in LCGD focusing on the Oliveira Mine geosite. As mentioned above, the gemological dis- trict covers an area of about 500 square kilome- ters, but the Oliveira mine was chosen as the geo- site, because of its amethyst mega geodes, location near a village, accessibility, and the support of the mining entrepreneur. It is located in the southeast of the department of Artigas, about 80 km from the city of Artigas, on a local road that connects by 15 km to the National Route #30. The relief in the area has typical features of a basaltic pla- teau, with an altitude of about 200 m above mean

sea level. The Oliveira Mine Geosite is made up of a series of large (6–10 m wide by 3 m high) galleries over 1000 m in length. There are several in-situ amethyst irregular-shaped to oblate geodes (decametric to metric sizes) on massive dark gray basalt belonging to colada (or spill) # 4. Although the site has no legal protection, both mining and tourism operators have committed to maintaining the abandoned mine in a condition suitable for vis- its and education, without extracting gems from the mine in the future. The mine is equipped to receive groups of tourists with safety equipment, accompanied by local guides and led through the galleries to the exhibition and events (cultural, ed- ucational) rooms.

Salles (2023) was the first to show the scientific, didactic and touristic values of this geosite in a geopark project in that region (Botucatú Mining Geopark Project). Los Catalanes Gemologic Dis- trict represented by de Oliveira Mine in the quan- titative assessment of scientific value according to Brilha (2016) scored as a very important geosite, corroborating the IUGS decision.

Deposits of Amethyst Conservation And Valo- rization Initiatives

The Catalanes creeks in northern Uruguay are in a region with a mining tradition of more than a century. Currently, 30 mining companies employ- ing hundreds of workers are producing world- class amethysts in about 80 quarries and mines. Three entrepreneurs (Mining Safari, Mining Tour and Los Catalanes Glamping) currently support geotouristic activities in abandoned mines. In ad- dition, this district is one of the most important areas with archeological vestiges mainly from the supply of lithic material (gems and silicified sandstones) to produce both jewelry pieces and projectile points by early human cultures since the Pleistocene-Holocene transition (Suárez 2014). It is for these reasons that, in certain areas of the dis- trict, initiatives for visualization and valorization

Los Catalanes Gemological District is defined as a complex area site sensu Fuertes-Gutiérrez & Fernández-Martínez (2010). Within this complex site, the Oliveira mine stands out by its exposure, number of galleries, size and quality of in situ ge- odes and gems. Two geologically important as- pects of these deposits are related to the mining of gemstone resources (prospecting, exploration, mining methods, environmental impact) and sci- entific research on magmatic processes in pre- served mining areas. An initiative to preserve part of the district in Oliveira mine has been developed by private entrepreneurs and contributes to geo- scientific knowledge and geoconservation (Brus- chi & Coratza 2018). Both touristic and mining entrepreneurs have even applied for and received funding to develop educational and tourist proj- ects (Fig. 8A), improve infrastructure and develop internal interpretive signage (i.e., Tourism Min- istry, Innovation and Research National Agency, Development National Agency, Fig. 8B).

A new cultural center called the Stone Museum (http://www.museos.gub.uy) is currently under construction in Artigas City with funding from the Ministry of Culture. Among other initiatives, the Botucatú Mining Geopark project located in northern Uruguay stands out, with amethyst de- posits in Oliveira mine geosite as one of its main sites of geological interest.

Conclusions

The presentation of the “First 100 IUGS Geolog- ical Heritage Sites” in the context of the Interna- tional Geoscience Programme of UNESCO is an important contribution to broader recognition of geoconservation worldwide (IUGS 2022). The designation of the amethyst deposits of Los Cat- alanes Gemological District (Artigas Department) as the first Uruguayan IUGS Heritage Site is an

Figure 8. Valorization and interpretation. (A) Tourists visiting Oliveira mine Geosite (B). Information panel explains gemstone characteristics and usages. Photos: Mateo Acosta.

important milestone for Uruguay. It is also a mark of recognition for the geoscience community and the promotion of research in geological heritage and the beginning of its geoconservation in the country.

Acknowledgments

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