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Medicinal
Waters
What is a medicinal water
source?
A medicinal spring is a natural source of groundwater that
contains minerals or other physicochemical characteristics
that may have beneficial effects on health. These properties
depend on multiple factors:
-The type of rocks that cross the water.
-The time that passes underground.
-The temperature it reaches.
-The disuel gases that drag.
Since ancient times, civilizations such as the Roman or Greek
have used these manantiales for therapeutic, religious and
social purposes. Today, its analysis allows us to understand
the interaction between geology, hydrogeology and human
health.
Classification of medicinal waters
Waters are classified according to three main criteria:
temperature, pH and mineral composition.
1. According to temperature
Type
|
Temperature (°C) |
Cold
|
<
20 °C |
Hypothermals
|
20
– 35 °C |
Mesothermals
|
35
– 45 °C |
Hyperthermal
|
>
45 °C |
2. According to pH
| Type |
pH range |
| Acidic
|
<
6.5 |
| Neutral |
6.5 – 7.5 |
| Alkaline
|
>
7.5 |
3. Second dilute minerals
Type of
water
|
Main
minerals |
Associated
properties |
| Bicarbonates
|
HCO₃⁻
|
Digestive,
diuretic |
| Sulfated
|
SO₄²⁻
|
Hepatic, mild
laxatives |
| Chlorinated
|
Cl⁻ |
Rehydrating,
metabolic stimulation |
| Ferruginous
|
Fe²⁺ |
Antianemic |
| Carbogases
|
CO2
|
Stimulants
digestive |
| Sulfurous
|
H2S
|
Dermatological,
antirheumatic |
| Radioactive
(natural) |
Radon
(Rn)
|
Sedating,
relaxing (in safe doses) |
Geological
origin of medicinal waters
Medicinal waters are not simply filtered rainwater. Its origin
implies deep and slow geological processes that can last years
or even seconds. The typical process follows these phases:
Infiltration: Meteoric water (rain or snow) penetrates
the subsoil through gaps, fissures or porous materials.
Deep circulation: The water descends hundreds of
thousands of meters, being heated by the geothermal gradient
(3°C per approximately 100m) and dissolving minerals from the
rocks.
Ascension: Through falls, fractures or permeable zones,
water returns to the surface, loaded with minerals, gases
(such as CO? or H?S) and, sometimes, natural radioisotopes
such as radon.
Key geological factors:
Type of rock (lithology): Caliza rocks, for example, favor the
appearance of bicarbonated waters, while volcanic rocks can
give rise to sulfurous or ferruginous waters.
Tectonic fracture: The falls and fractures allow the
circulation and emergence of water at the surface.
Residence time: The longer the water spends in the
underground, the more mineralized it will be.
Internal heat: In volcanic or geothermally active areas, water
can reach temperatures above 50°C.
In short, each spring is the result of a unique geological
history, and its study allows us to read that history through
water
Granite
Dissolution Process
1) Formation of carbonic acid
Water + CO₂ from the soil → H₂CO₃ (carbonic acid)
2) Hydrolysis of granite minerals
The acid penetrates the granite and reacts with its minerals.
Dissolution of specific minerals:
Feldspars (K,
Na, Ca)
Reaction:
feldspar + H₂CO₃ + H₂O → clays + K⁺, Na⁺, Ca²⁺, Si(OH)₄, Al³⁺
Result: Formation of clays and release of ions into water.
Micas (biotite, muscovite)
Release: K⁺, Mg²⁺, Fe²⁺/Fe³⁺, Al³⁺ → also contribute to clays
and dissolved ions.
Quartz (SiO₂)
Very resistant → low dissolution, usually remains as a residue
Mondariz
Spa Resort
The Mondariz Spa Resort
is located between the municipalities of Mondariz and
Mondariz-Balneario, both in the southeast of the province of
Pontevedra. It is nestled in the valley of the Tea River (Red
Natura) and its tributaries, the Xabriña and Aboal. Spa and
bottling activities are the main sources of income for the two
aforementioned municipalities and the surrounding areas.
Mondariz's importance as a spa resort dates back to Roman times,
when the territory belonged to the city of Búrbida.
Geological
Context
On a local scale, we can
say that the Mondariz area is dominated by igneous and metamorphic
rocks typical of the Hesperian Massif, ranging in age from the
Precambrian to the Devonian-Early Carboniferous. Specifically,
Mondariz is located within the Meridian Depression Geological
Unit, which corresponds to a large strip, thirty kilometers wide
in a north-south direction, connecting Carballo with Tui and
featuring various mineral and thermal springs associated with
fractures in alkaline granites.
Specifically, the area in
which Mondariz is located is characterized by the presence of
igneous rocks in the form of medium- and fine-grained equigranular
granites, corresponding to a two-mica alkaline granitic species.
This granite material
appears highly fractured throughout the area, especially at this
point, as it corresponds to the intersection of two faults: the
main one (NW-SE) that extends to distant areas, and another
(NE-SW) that cuts the former at this location.
Therefore, at the Mondariz Spa, based on its geological and
hydrogeological characteristics, we find a deep flow
hydrogeological pattern.
This is associated with the two-mica granites and the cutting of
the faults within them. The discharge occurs over a thin layer of
Quaternary sedimentary material associated with the Tea River
Valley, with lower hydraulic potential at this point.
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