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Gas migration from two mine districts: The Tolfa (Lazio, Central Italy) and the Neves-Corvo (Baixo Alentejo, Portugal) case studies
Language
English
Obiettivo Specifico
6A. Monitoraggio ambientale, sicurezza e territorio
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/152 (2015)
ISSN
0375-6742
Publisher
Elsevier Science Limited
Pages (printed)
37-53
Issued date
February 7, 2015
Keywords
Abstract
Detailed soil gas surveyswere conducted at twomine districts to understand gas migrationmechanisms fromdeposits
buried at different depths. The Tolfa (Lazio, Central Italy) and Neves-Corvo (Baixo Alentejo, Portugal) mine
districts have different characteristics: the former is relatively shallow (30–100 m) whereas the latter is at a
depth of 400–500 m and covered by low-permeability metamorphic rocks. The studied gases included major
(N2, O2, CO2) and trace (4He, 222Rn) gases, hydrocarbons (CH4, C2H6 and C3H8) and S compounds (H2S, COS,
SO2). The measured concentrations (some examples of max values at Tolfa: Rn 233 Bq/L, CO2 9.5%, CH4
12.3 ppm, COS 3.7 ppm; and at Neves-Corvo: Rn 130 Bq/L, CO2 24.3%, CH4 0.1%) indicate that gases migrate preferentially
through zones of brittle deformation by advective processes, as suggested by the relatively high rate of
migration needed to obtain anomalies of short-lived 222Rn in the soil pores. Considering the different depths of
the two ore deposits, obtained results can be considered as features of near-field (Tolfa) and far-field (Neves-
Corvo) gas migration.
buried at different depths. The Tolfa (Lazio, Central Italy) and Neves-Corvo (Baixo Alentejo, Portugal) mine
districts have different characteristics: the former is relatively shallow (30–100 m) whereas the latter is at a
depth of 400–500 m and covered by low-permeability metamorphic rocks. The studied gases included major
(N2, O2, CO2) and trace (4He, 222Rn) gases, hydrocarbons (CH4, C2H6 and C3H8) and S compounds (H2S, COS,
SO2). The measured concentrations (some examples of max values at Tolfa: Rn 233 Bq/L, CO2 9.5%, CH4
12.3 ppm, COS 3.7 ppm; and at Neves-Corvo: Rn 130 Bq/L, CO2 24.3%, CH4 0.1%) indicate that gases migrate preferentially
through zones of brittle deformation by advective processes, as suggested by the relatively high rate of
migration needed to obtain anomalies of short-lived 222Rn in the soil pores. Considering the different depths of
the two ore deposits, obtained results can be considered as features of near-field (Tolfa) and far-field (Neves-
Corvo) gas migration.
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