CordMinAge 2005:Isotopic ages for significant mineral deposits of the Canadian Cordillera
Recommended citation:
Madsen, J.K., Breitsprecher, K. and Anderson, R.G. (compilers), 2005. CordMinAge 2005: Isotopic ages for significant mineral deposits of the Canadian Cordillera. Geological Survey of CanadaOpen File 4969, Release 1.1. Release date: August 18, 2005, 1.9 Mb
OVERVIEW
This product (CordMinAge 2005)is a database of basic deposit information for geologically significant metallogenic deposits of the Canadian Cordillera, combined with new assignment of “best constraint on timing” for those deposits, derived from assessment of isotopic-age determinations available in the vicinity of the deposit. 354 deposits are presently included in this data-base, for which 292have been assessed for age. Assessment and assignment of age constraint for the remaining 62 deposits is anticipated for a future release of this product. For this first release of the product, age assessment has been targeted and is complete for all porphyry deposits, and deposits of Jurassic age. Biostratigraphic information for deposits whose age may be closely constrained by fossils in enclosing host rocks (e.g. SEDEX, VHMS types) are not included in this preliminary compilation.
Metallogenic deposits are identified as “geologically significant” on the basis of their inclusion in the earlier synthesisof same by Dawsonet al. (1991),with additionsfor porphyry style and Iskut mapsheet area (104B) deposits based on current views of deposit geology. Deposit information provided herein is taken directly from the Minfile databases of the British Columbia Geological Survey Branch ( and of the Yukon Geological Survey ( Isotopic age information was based on querying the comprehensive data-sets of same provided in the recently released open-file BCAge 2004A and YukonAge 2004 databases (Breitsprecher and Mortensen, 2004a, b). These two databases include ages reported to May 2004; thus subsequently reported isotopic ages have not been assessed in this release of the product.
The database was designed for viewing in Microsoft Access 2002® (component of MS Office XP Professional®), which must be installed on the user’s PC for full functionality. Flatfile versions of content are included on the CD as Microsoft Excel® format tables, which enable viewing of contents by users without MS-Access, but are not functional in terms of querying/ relational linking capabilities, those being features of MS-Access.
DESCRIPTION OF CONTENT
The deposit information included for each mineral occurrence in the database derives directlyfrom the British Columbia Minfile and Yukon Minfile databases. This information constitutes the compiled fields,including: deposit name, status, district, location, specific type(s)(mineral profile), deposit note, commodities, tectonic belt, and plutonic suite/lithology. The age/timing information is added for each deposit by the compilers. The new information fields include: isotopic ageand related information, time-scale assignment(based on the timescale of Okulitch, 2004), agenote, reliability and relevance, generic type, and data source.
Compiledfields:
ID tag#: internal database number required by Microsoft Access®database program to track deposits and to link to Commodities subfile but is of no use to, and should not be edited by, the user.
deposit name/associated camps: “deposit name” is the most common name for the deposit in current use, to the best of the compilers’ knowledge. The “associated camps” field provides a means to filter or group deposits on a district basis.
minfile#: the Minfile ID number assigned in the B.C. or Yukon minfile databases for the particular deposit. For larger deposits (e.g. porphyry camps), a specific mineral occurrence was selected from the Minfile database to represent the deposit. This enables output of location information for groups of deposits, filtered by age and/or type and/or commodity, to map plotting applications for the production of large scale maps.
status:showing, prospect, developed prospect, past producer – as listed and defined in B.C. and Yukon Minfile compilations.
jurisdiction/district:“jurisdiction”identifies the province or territory in which the deposit occurs. “District” refers to mining district, as listed in Minfile records.
type-specific: the detailed deposit-type assignment as given in Minfile. Note that BC and Yukon use different classification/coding systems for deposit type; we have retained those herein to facilitate users searching on the basis of known class types. However, searching eg. “L04” types, which returns porphyry systems under BC’s Minfile classification, will not “hit and return” applicable porphyry records from Yukon. To this end, we provide a new generic field which can search across both jurisdictions using simpler terminology than Minfile classification schemes provide (see “type-generic” in following section).
commodities: a listing of the full-name (eg. “lead” not Pb, “gold” not Au) for all commodities reported for the deposit, as listed in Minfile records. The commodities are listed in order from most to least important for that particular deposit.
location fields:separate fields for location in latitude and longitude and as theNational Topographic System (NTS)listing of the deposit in its one million-scale, 1:250 000 scale,and, 1:50 000 scale location designations. Universal Transverse Mercator(UTM) zone, easting, northing, with the North American Datum (NAD) projection (NAD27 or NAD83) given in the field labeled “NAD:”. These coordinates are taken from the B.C. and Yukon“Minfile” databases. Latitude and longitude are listed in separate degrees, minutes, and seconds (dd-mm-ss) fields again for easeof filtering from the Access interface and data import to map plotting applications.
deposit note:summary, or overview text, as provided in the from B.C. and Yukon minfile databases.
geologic unit/terrane/belt/plutonic suite: where available, this information taken from B.C. and Yukon minfile or BCAge/YukonAge databases, whichever provides the more up-to-date and/or specific information.
New information fields:
isotopic age:This field provides the compilers’ assessment of the best available isotopic age, either as a direct mineralization age (commonly the isotopic age of the host rock, e.g. for porphyry deposits) or that which provides a constraint on the mineralization age. The ages and age interpretation (i.e. mineralization age, igneous crystallization age, cooling age, etc.) derive from the BCAge 2004A1 and YukonAge 2004 databases of isotopic ages. The isotopic age assessment ranges from:
i)“direct” to “estimated”, being terminology which reflects the analytical quality (precision, overall reliability) of the age
ii) “metasomatic” to “inferred”, being terminology which reflects the degree to which the cited age is known to relate to the mineralization event
Further notes regarding age assessment and assignment are provided in the “age note” and “reliability/relevance” fields (see explanations below).
Note: This preliminary release of CordMinAge 2005 contains 62 deposits whose mineralization ages have not yet been assessed, but which are nonetheless includedon the basis of their status as historically or potentially significant deposits.These deposits can be identified from a blanket descriptor in “age note” field (see below), to distinguish un-assessed deposits from those for which there is no proximal isotopic age available.
method/age interp:These fields are extracted from BCAge and YukonAge databases for each applicable age pulled therefrom. Age method refers to the isotopic system(s)used to determine the age, and the mineral or material which was dated. Isotopic systems include: U-Pb, Ar-Ar, Re-Os, K-Ar, Rb-Sr, Sm-Nd, Pb-Pb. The “age interp” field indicates geologic significance of the age determination age, and includes: igneous crystallization age, igneous cooling age, cooling age, mineralization age, and alteration age,
age note: This field provides a brief explanation of the compiler’s methodology and justification for choosing the age as being the best available constraint on mineralization age. Variations in geologic knowledge, isotopic age availability, and quality of available ages at each deposit prevent a single methodology from being employed for age selection. Therefore, this field provides means to explain justification for our choice - or limitations of it, as the case may be – on a case-by-case. Note that for many deposits, the only proximal isotopic ages available continue to be older K-Ar determinations. However, where possible, these ages are generally discarded in favour of the more recent, more precise and analytically superior isotopic ages (e.g., U-Pb dates). In the case of suspected analytical problems with the determination, the “age note” field will contains an additional note stating that the age is “B”-rated (suspect) in the parent BCAge or YukonAge database, and why. While the age may still be correct, users should employ caution in utilizing or relying upon those ages. Ages with a “C”-rating (known unreliability) in the BCAge or YukonAge databases have in no case been selected for use in this product. Finally, regarding the 62 un-assessed depositswhich are targeted for age assignment in a future release of this product, as noted in the Overviewsegment, the “age note” field contains the phase “Age assignment pending”.
relility/relevance: This field provides a two-word boil-down of the information contained in the “age-note” field, and thus gives a brief assessment of
i)The analytical reliability of the age determination:
- direct – the age is analytically sound, use with confidence. Equivalent to “A” rating in BCAge/YukonAge databases.
- estimate – the age is either analytically suspect or analytically imprecise:
- analytically suspect – there are known problems with specific isotopic system used, and/or suspect on the basis of a directassessment of raw analytical data. Equivalent to “B” rating in BCAge/ YukonAge databases, and transfers therefrom with each age as applicable.
- poorly constrained - high relative error. We choose a cut-off of ±2.5% as being “precise” versus “estimated”. This margin of error is lower than analytical error for K-Ar determined ages; hence all K-Ar ages are flagged “estimate”. This assessment is superimposed on the A/B rating system of the parent databases, which themselves do not individually rate ages on the basis of %error.
ii)The certainty with which the dated unit relates to the mineralization event. Uncertainties arise from unproven temporal association of a given intrusion to a proximal deposit, or from uncertain field relations, due to such things as poor exposure and/or lack of available high-resolution mapping in the area of the deposit. Mineralization at well-studied deposits may have well constrained ties to surrounding geology, while those which are understudied or which are situated in areas of poor regional mapping coverage may not. The ratings used herein, in decreasing order of known affinity between the age determination itself and the mineralization event, are:
- metasomatic– the age directly dates mineralized or alteration product in veins or stockwork hosting the commodity.
- host – the age dates the unit hosting the commodity. In cases of syn-genetic mineralization (see age-note and deposit-note fields), this descriptor provides a reasonable estimate of the time of the deposit’s formation. In cases where a syn-genetic relationship is unproven, this descriptor provides a maximum age of mineralization.
- maximum / minimum - these descriptors signify that the dated sample is from a unit with direct field-relationships to the mineralized body (eg. cross-cutting, underlying, overlying). See ‘age-note’ for specifics of field relations between mineralized and dated units.
- associated– this descriptor signifies that the age derives from an igneous unit which previous workers have interpreted to be responsible for, or otherwise associated with, mineralization of the deposit.See Minfile information regarding same in “deposit note”.
- inferred– this descriptor signifies that there is no available (reliable) age determinations matching any of the foregoing categories, but other dated units in the region may suggest a possible correlation for the particular mineral deposit (e.g., an age from a proximal intrusion is a likely candidate for triggering metasomatic processes, but has untested correlation to the mineralization event). Inferred age assignments require the user to conduct further research specific to the deposit of interest, beyond the scope of this compilation, to verify the applicability of the age to the mineralization event.
era/period/epoch/stage: These fields have been provided to enhance search or filtering functions of the dataset. The new isotopic age assignment for a particular mineral deposit in CordMinAge 2005 is taken as the best indicator of time-scale placement for the deposit, and supercedes information given in other sources, such may be given in the Minfile databases. The time-scale used in CordMinAge 2005 is that of Okulitch (2004).
ageref: This field provides a reference ID_#, internal to the database, which links citation information for the source of each age quoted in CordMinAge 2005. Thus, this field contains an ID-number for all deposits which have a corresponding isotopic age, and is blank for those where no isotopic age is available, or for those which have yet to be assessed for age assignment. If the raised button contains a number, “click” to view the age-reference pop-up, which provides the full citation for the report the age determination appears in.
type-generic: This field assigns mineral deposit types internally consistent to the database, necessary because BC and Yukonminfile datasets categorize deposit types differently. The mineral deposit type descriptors unique to B.C. or Yukon have been retained in the “specific type” field, so that end users familiar with that terminology may continue to use it to filter deposit types. Generic type allows the user to filter or query the database for deposits found in B.C. and Yukon using the following deposit-type classes:kimberlite, MVT, placer, porphyry, sedimentary, skarn, ultramafic, vein, volcanic
source: This field specifies the basis for inclusion of the particular deposit as being historically, presently or potentially “significant”. All deposits included in the compilation of Dawson et al.(1991, Fig. 19.1) are included herein; the source field also indicates which panel of their Figure 19.1 (e.g., a, b, c …)lists the deposit. Additional deposits were included based on suggestions by D. Sinclair (porphyry deposits) and R.G. Anderson (IskutRiver area). Such deposits are marked by the Geological Survey of Canada project code which funded this compilation (X15-MinSyn), followed by the name of person recommending its inclusion.
BCAge/YukonAge age ID: This field identifies the age determination record in the parent database (BCAge or YukonAge). The number provided herein is the age-record “id-tag” from the parent database, which the user can look up independently within those databases for further information regarding the dated sample. The field is not hyperlinked or integrated to the BCAge/YukonAge databases; rather the user will manually query for it from within those databases, if further information is desired. To do this, open the appropriate parent database for the jurisdiction (BCAge for BC deposits, or YukonAge for Yukon deposits); power search for all records (“byage” function, then input 0 to 9999 as min/max criterion); filter on the “ageno” field, as explained in “usage notes” below, with the age-tag number provided herein as the filter criteria. (See “General Usage Notes” below for tips and examples on using MS-Access filtering functions.)
Mineral synthesis project ID tag: This field is for future GSC internal use, upon integration of similar nationwide regional databases into the national “significant deposits” metadata structure. The field will be used to identify these deposits within the larger dataset, following completion of the national “Mineral Synthesis” compilation.
GENERAL USAGE NOTES
The “deposits” interface window displays all the fields pertinent to this database. You may scroll through the deposits one-by-one, either by using the page-up / page-down buttons on your keyboard, or by using the CD-control buttons at the bottom of the form.
Use MS-Access filtering tools (right click functions on mouse, or from the Access file menu at top of window) to enhance searchingand querying of the database. For example, you can filter for specific types of deposits (e.g., porphyry only), or for deposits on a specific mapsheet (eg. 104B only), or those with a specific name, or those with a specific type of commodity. With cursor in the information field to be filtered [left-click the info field], activate filter functions by [right-click], or [choose “records” “filter” from Access menu bar]. Now, enter your filter criterion, using wildcard characters [*]before and/or after your specified contentas given in the examples below (MS-Access filtering is not Boolean; wildcards required). The selected subset of records can be re-filtered, to further winnow the returned deposits to a more precise range of interest. Because each filter command acts thus (searching only on the last subset of records retrieved, vs. the whole database), it is necessary to “reset” the form to “all deposits” prior to beginning a new query (vs. building on the last one). Reset the deposits to “all” by [right-click] anywhere in the form window, then choose [remove filter/sort]. A properly reset database will say “1 of 354 records” at the bottom-left corner of the window, vs. some smaller number of records returned by your previous query.