Tom Heldal - Academia.edu (original) (raw)

Papers by Tom Heldal

Federal Institute for Geosciences and Natural Resources (BGR), Germany (1); National Laboratory o... more Federal Institute for Geosciences and Natural Resources (BGR), Germany (1); National Laboratory of Energy and Geology (LNEG), Portugal (2); Geological Survey of Denmark and Greenland (GEUS), Denmark (3); Geological Survey of Spain (IGME), Spain (4); Geological Survey of Norway (NGU), Norway (5) <br> <br>"Raw materials, you can't do well without them". This statement echoes the needs for a reliable raw materials supply chain. Awareness of raw materials is an essential element for the manufacturing industry, infrastructure, digitalisation, and others has significantly increased in this decade. So did the demand. The specific physical and chemical properties of the chemical element and the minerals they form make mineral raw materials special. The mineral surface reactivity for example, is an important parameter for pharmaceuticals [1]. COVID-19 refocused attention on the antibacterial behaviour of copper and copper alloys.

The geological history of Norway is a complex one, . The exploitation of geological resources of ... more The geological history of Norway is a complex one, . The exploitation of geological resources of different kinds has always provided the backbone of the Norwegian community. Nevertheless, the perception of geology and the geological processes that created the landscape is little appreciated, compared to bio-diversity and cultural heritage. Some geological localities play an important role in our perception and scientific understanding of the landscape. Other localities are, or could be, important tourist destinations. Other localities can in turn be important for geoscience education on all levels, whereas other plays a major role in the understanding of geodiversity and geoheritage and should be protected as natural monuments. A database based on old registrations has been compiled and a web mapping server is recently launched based on old and new registrations. However, no systematical classification and identification of important sites has been done for the last thirty years. We...

Metamorphic flagstones are characterised by a regularly spaced mica foliation separated by quartz... more Metamorphic flagstones are characterised by a regularly spaced mica foliation separated by quartzo-feldspathic domains, along which the rocks can be cleaved into commercial slabs. In the thrust nappes of the Scandinavian Caledonides, such deposits are essentially developed from psammitic rocks in high-strain zones. Recent investigations have shown that the industrial quality of many flagstone deposits can be linked to several aspects of the tectonometamorphic development of the rocks, and especially to rapid vertical and lateral variations in strain. Field relations and microtextures from three different flagstone deposits are described and used as examples. Finally, a structural and textural characterisation of flagstones is proposed.

Several building-stone quarries and prospects in Eritrea were visited during September 1998, as a... more Several building-stone quarries and prospects in Eritrea were visited during September 1998, as a part of the Norwegian-Eritrean ERINOR co-operation project. The bedrock geology of Eritrea comprises a variety of rocks, of which Proterozoic granitoids and marbles are, at present, considered to be most interesting for building-stone production. Neither the marble deposits nor the granitoids visited are of such exclusive quality that they would obtain high prices on the international dimension-stone market. However, several deposits seem to be of excellent quality for low-cost production of slabs, tiles and other products, and thus represent an interesting resource for domestic processing.

Background Tolstadkvernberget, located in the municipality of Vågå, central South Norway (Fig. 1)... more Background Tolstadkvernberget, located in the municipality of Vågå, central South Norway (Fig. 1), has long been recognised as one of the significant quarries in Norwegian millstone history (Brekken 1980, Teigum 2011). Much of the quarry landscape was subject to a preservation order in 1987, in compliance with the Norwegian Cultural Heritage Act, as an important cultural heritage site for ancient millstone production. Historical sources show that the quarries were already worked in 1426 and record apparently continuous activity until the end of the 19th century, a period of nearly 500 years or more (Brekken 1980, Teigum 2011). Covering the apparent time gap between large-scale quarrying at Hyllestad and Salten in the Viking Age to the High Middle Ages1 and at Selbu in the Modern Period (Baug 2002, Heldal & Bloxam 2007, Grenne et al. 2008, Grenne et al. this volume), Tolstadkvernberget thus provides an important account of a period of Norwegian millstone quarrying that otherwise lies...

Introduction During the 1980s and early 1990s, several investigations focused on the complex tect... more Introduction During the 1980s and early 1990s, several investigations focused on the complex tectonostratigraphy in the western part of the Helgeland Nappe Complex (HNC). Important discoveries were made, such as the recognition of a number of ophiolite fragments and a primary, angular unconformity between the ophiolites and metasedimentary cover sequences. The ophiolite fragments were correlated with other Late Cambrian-Early Ordovician ophiolites in the Caledonides, including the Leka Ophiolite Complex (Fig. 1). Several of these ophiolites have yielded ages of 500-485 Ma (Dunning & Pedersen 1988). Other metasedimentary rocks in the area include migmatite (mica) gneiss, calc-silicate gneiss and marble interpreted to represent remnants of a Neoproterozoic continental margin sequence. Both sedimentary successions have been affected by pervasive deformation and medium-grade metamorphism, and primary features are, in most areas, totally obliterated. However, on some small islands to the...