This document discusses hydrothermal fluids and hydrothermal ore deposits. It begins by describing the different types of fluids found in the Earth's crust, including sea water, meteoric water, connate water, metamorphic water, and mixtures. For hydrothermal deposits to form, these fluids need to circulate through the crust to dissolve and transport metals. Common hydrothermal deposit types include veins and cavity fillings. Veins can be fissure, ladder, or gash veins and cavity fillings include saddle reefs. Metal solubility in hydrothermal fluids is controlled by factors like temperature, pH, and ligand complexes. Precipitation occurs when solubility decreases, such as due to changes in fluid composition or physical properties like

1. PREPAREDBY:
VARINDRA SAINI
MBM ENGINEERING COLLEGE JODHPUR

2. S.NO. TOPIC PAGE NO.
1 INTRODUCTION 1
2 ORIGINS OF HYDROTHERMAL SOLUTION 1
3 OTHER FLUIDS IN THE EARTH’S CRUST AND THEIR
ORIGINS
2
4 THE MOVEMENT OF HYDROTHERMAL FLUID IN THE
EARTH’S CRUST
3
5 NATURE OF ORE FORMING SOLUTIONS 4
6 DISSOLUTION OF METAL IN SOLUTIONS TO FORM
DEPOSITS 4
7 PRECIPITATION MECHANISMS FOR METALS IN
SOLUTION
5
8 DIFFERENT TYPES OF HYDROTHERMAL DEPOSITS 6-11
9 Cl COMPLEXATION OF Zn 12
10 CONCLUTION 13

4. In addition to magmaticfluids, there are four other major
water types on or near the Earth’s surface. Although they
may allhave had similar origins, each of these fluid
reservoirsis different in terms of its composition and
temperature and will, therefore, play differentroles in the
formation of ore deposits. The major water types are defined
as sea water, meteoric water, connate water and metamorphic
water,listed typically in order of increasing depth (and
temperature) in the crust. A fifth fluid reservoir,where
waters are derived from a mixing of two or more other water
types, is also described below,specifically because mixed
fluids can be very important in certain ore-forming
environments.

5. In order to be effective as a mineralizing
agent,hydrothermal fluids need to circulate through the
Earth’s crust. The main reason for this is that
they need to interact with large volumes of rock in
order to dissolve and transport the metals required to
form hydrothermal ore deposits. The flow of an ore
fluid should preferably be focused so that the dissolved
constituents can be concentrated into an accessible
portion of the Earth’s crust that has dimensions
consistent with those of a potential ore body

6. Fluid inclusions in mineral grains preserve samples of hydrothermal solutions. Upon
cooling, the hydrothermal brines separate into solid (usually NaCl,gas (CO2 + CH4) and
aqueous phases.The temperature at which the fluid was trapped can be determined by
heating the sample and measuringthe temperature at which gas + liquid recombine

7. It is possible to stabilize many different metal–ligand complexes under wide
ranging conditions in natural hydrothermal solutions, thereby promoting the kind
of solubility levels required to make effective oreforming fluids. Once a metal is in
olution, however, it then needs to be extracted from that fluid and concentrated in a
portion of the Earth’s crust that is sufficiently estricted and accessible to make an
economically viable ore body. It is obvious that a wide range of precipitation
mechanisms are ikely to be effective since any mechanism that will destabilize a
metal–ligand complex and, therefore, reduce the metal solubility, ill cause it to be
deposited in the host rock through which the hydrothermal solution is passing.
At shallow crustal levels ore deposition will take place by open space filling,
whereas deeper down where porosity is restricted, replacement of existing minerals
tends to occur. Decrease in temperature is the factor that, intuitively, is regarded as
the most obvious way of promoting the precipitation of metals from hydrothermal
fluids. At depth, however, temperature gradients across the structures within which
fluids are moving tend to be minimal and metal precipitation will be neither
efficient nor well constrained to a particular trap zone. Deposition of metals in
such a case is achieved more effectively by changing the properties or composition
of the hydrothermal fluid. If ore solution occurs by metal–chloride complexing
then precipitation could occurvery efficiently by increasing the pH of the ore fluid.

8. Hydrothermal deposits occurin a variety of shapes and sizes .the most common
forms are veins and cavity fillings.
VEINS
Veins are narrow ,elongated or tabular shaped economic minerals occurring within
host rock. Veins are further classified into following types:
 Fissure-veins
 Ladder-veins
 Gash-veins
 Stock works
CAVITY FILLINGS
Cavity fillings are ore deposits that get deposited from the hydrothermal fluids
inwell defined open spaces ( cavities ) other thanalong cracks or fractures available
in the hostrock.
Saddle reef is an intresting cavity filling .In saddle reef cavities are associated with
folded rocks and minerals get deposited in such cavities

9. VEINS :
Fissure veins
Ladder veins

10. Gash veins
Stockwork

11. CAVITY FILLINGS :
Saddle reef
Widely disseminated
vein networks of
Sulfide Cu Deposis,
Waraz area,
NE-Iraq
Kurdistan Region

12. Hydrothermal
vein deposits

13. Note: the distribution of hydrothermal ore
deposits are irregular in the host rocks
Formation of hydrothermal deposits

14. Zn+2 + Cl- = ZnCl+
Zn+2 + 3Cl- = ZnCl3
-
Zn+2 + 2Cl- = ZnCl2
Zn+2 + 4Cl- = ZnCl4-2
Zn(H2O)6 + nCl = ZnCln + 6H2O
pK = -0.2; H = 43.3 kJ/mol
pK = -0.25; H = 31.2 kJ/mol
pK = 0.02; H = 22.6 kJ/mol
pK = -0.86; H = 5.0 kJ/mol

15. Thus at the end of the projectwe can conclude that Hydrothermal mineral
deposits are those in which hot water serves as a concentrating,
transporting, and depositing agent. They are the mostnumerous of all
classes of deposit.
It is interesting to know that Hydrothermal deposits are never formed from
pure water, because pure water is a poor solvent of mostore minerals.
Rather, they are formed by hot brines, making it more appropriate to refer
to them as products of hydrothermal solutions. Brines, and especially
sodium-calcium chloride brines, are effective solvents of many sulfide and
oxide ore minerals, and they are even capable of dissolving and
transporting native metals such as gold and silver
Hydrothermal depositvarious useful and precious elements like gold ,
copper, tungsten,molybdenum and to some extent silver , lead and zinc
etc. Formation of hydrothermal ore deposits is linked not only to the generation of
significant volumes of fluid in the Earth’s crust, but also to its ability to circulate
through rock and be focused into structural conduits (shear zones, faults, breccias,
etc.) created during deformation. The ability of hydrothermal fluids to dissolve
metals provides the means whereby ore-forming constituents are concentrated in
this medium. Temperature and composition of hydrothermal fluids (in particular
the presence and abundance of dissolved ligands able to complex with different
metals), together with pH and fO2, control the metal-carrying capability of any
given fluid. Precipitation of metals is governed by a reduction in solubility which
can be caused by either compositional changes (interaction between fluid and rock,
or mixing with another fluid), or changes in the physical parameters (P and T) of
the fluid itself. Economically viable hydrothermal ore deposits occurwhen a large
volume of fluid with a high metal-carrying capacity is focused into a geological

16. location that is bothlocalized and accessible, and where efficient precipitation
mechanisms can be sustained for a substantial period of time.
INTRODUCTION TO ORE FORMING PROCESS
:by Laurence robb
ENGINEERING GEOLOGY
:by Praveen singh