Ore Grade/Tonnage Estimator: Multi-Block Tonnage & Weighted Grade

Ore Grade / Tonnage Estimator

Multi-block reserves · weighted grade · cutoff filter

Units & Method

All three combine block areas the same simple way here — enter each polygon/triangle as a block. Geostatistical methods (kriging) are out of scope.

Ore Blocks (★ add freely)

Cutoff Grade (optional)

Blocks below cutoff are classified waste and excluded from the reserve. Leave blank to include all.

Result

Add your ore blocks with area, thickness, specific gravity and grade to get total tonnage, the tonnage-weighted average grade, metal content and a per-block breakdown — with an optional cutoff grade splitting ore from waste

Tonnage here is volume times specific gravity, and the average grade is tonnage-weighted — each block contributes in proportion to its mass, which is why a large low-grade block pulls the average down more than a small one, and why a simple mean of grades is wrong whenever blocks differ in size. Specific gravity should be lab-measured on your own ore whenever possible: the built-in reference values are broad typical ranges, and in-situ bulk density also differs from solid-rock SG through porosity, moisture and voids. The cutoff comparison shows how the economic threshold reshapes the reserve, but real cutoff decisions also involve mining, processing and price assumptions. This is a basic deterministic estimate for study and preliminary work — resource and reserve reporting for investment purposes must follow recognised codes (JORC, NI 43-101, SAMREC) with geostatistical estimation and a competent person sign-off.

Ore Grade/Tonnage Estimator: Multi-Block Reserves with a Properly Weighted Average Grade

A real ore body is never one uniform block, it’s made up of several sections, each with it’s own area, thickness, density and grade, and averaging those grades the wrong way can genuinely misstate your whole reserve. This ore reserve calculator lets you add as many blocks as your deposit actually needs, works out each one’s own tonnage from area times thickness times specific gravity, and then combines them using a proper weighted average grade calculator approach, each block pulls the overall average in proportion to it’s own tonnage, not just it’s grade number sitting there on it’s own. An optional cutoff grade splits your blocks into ore and waste, so you see exactly how that one economic decision reshapes the reportable reserve. Both metric and imperial units are supported, short or long tons either way and grade can be entered as percent or g/t, with metal content coming out in tonnes, kilograms or troy ounces depending on what actually makes sense for your metal.

How to Use

Step 1: Set your units and method
  • Select your Unit System: Metric (m², m, tonnes) or Imperial (ft², ft, tons). If you pick Imperial, a Ton Type dropdown appears, Short ton (2000 lb) or Long ton (2240 lb).
  • Select your Grade Unit: % for base or industrial metals, or g/t for precious metals.
  • Select a Method label: Simple Block-Average, Polygonal, or Triangular. All three actually combine your block areas the same simple way in this tool, you just enter each polygon or triangle as it’s own block, this label is really just for your own record-keeping, since full geostatistical methods like kriging are out of scope here.
Step 2: Add your ore blocks
  • Tap Add Block for each section or drill-hole area in your deposit. For every block, enter it’s Area, Thickness, Specific Gravity and Grade.
  • If you don’t have a measured specific gravity yet, use the SG reference dropdown to fill the last block with a broad typical value for common ore types, then replace it with your own lab-measured figure as soon as you have one, since real in-situ density can differ quite a bit from a textbook range.
  • Repeat for every block in your deposit, there’s no limit on how many you can add.
Step 3: Add a cutoff grade, if you want one
  • Under Cutoff Grade (optional), enter your Economic Cutoff Grade. Any block below this grade gets classified as waste and dropped out of the reserve. Leave this blank if you just want every block included.
Step 4: Estimate and read your result
  • Tap Estimate Reserve. The result shows total tonnage, the tonnage-weighted average grade across all your blocks, total metal content in tonnes, kilograms or troy ounces, a full per-block breakdown and, if you set a cutoff, a side-by-side comparison of the filtered ore-only reserve against the unfiltered total.
Step 5: Export
  • Use Print / PDF for a clean printable copy or Copy to paste the numbers into your reserve report.

Key Features

  • Fully custom multi-block entry, add as many ore blocks as your actual deposit needs, no fixed limit
  • Tonnage from area × thickness × specific gravity, calculated separately for every block
  • Proper tonnage-weighted average grade, not a naive average of grades, so large and small blocks contribute correctly in proportion to their own mass
  • Optional cutoff grade filter, splitting blocks into ore and waste, with a clear before/after reserve comparison
  • Metric and imperial units, including both short and long ton conventions
  • Percent or g/t grade support, with metal content shown in tonnes, kilograms, or troy ounces as appropriate
  • SG reference list for common ore types, always overridable with your own measured value
  • Export as PDF or copy the result.

Formula / Logic Used

Tonnage per Block

Tonnage=Area×Thickness×SGTonnage = Area \times Thickness \times SG

For imperial short or long tons, this volume is converted using a 62.5 lb/ft³ water reference, then divided by 2000 or 2240 lb depending on which ton type you selected.

Tonnage-Weighted Average Grade

Gradeavg=∑(ti×gi)∑tiGrade_{avg} = \frac{\sum (t_i \times g_i)}{\sum t_i}

This is why a large, low-grade block pulls the overall average down more then a small one does, and it’s exactly why a plain arithmetic mean of the individual grade numbers, ignoring tonnage entirely, gives a wrong answer whenever your blocks differ in size.

Metal Content

Metal=Tonnage×GradeMetal = Tonnage \times Grade

Cutoff Filter

Every block’s grade is compared against your entered cutoff, blocks at or above cutoff count as ore and stay in the filtered reserve, blocks below it are reclassified as waste and dropped, while the unfiltered total still shows every block combined for comparison.

if block_grade >= cutoff_grade: block counts as ore
if block_grade < cutoff_grade: block counts as waste, excluded from filtered reserve

Who Should Use This Tool

Mining and geology students and junior mine engineers doing a basic, deterministic reserve estimate from block or drill-hole data for study or preliminary work. This tool is explicitly a simplified estimator, not a substitute for full geostatistical estimation, actual resource and reserve reporting for investment purposes must follow a recognised code, JORC, NI 43-101, or SAMREC, with a competent person’s sign-off.

Frequently Asked Questions (FAQs)

1. Why can’t I just average the grade of my ore blocks directly?

A plain average treats every block equally regardless of size, so a small, high-grade block and a large, low-grade block would count the same, which don’t reflect reality since the large block actually contains far more total ore. This tool weights each block’s grade by it’s own tonnage instead, so bigger blocks correctly pull the average toward their own number more strongly.

2. How is tonnage calculated from area and thickness?

Multiply the block’s area by it’s thickness to get volume, then multiply by specific gravity to convert that volume into tonnage. This tool does this for every block you add and then sums them for your total reserve.

3. Why does specific gravity matter so much, and should I trust the built-in reference values?

Specific gravity is what converts a purely geometric volume into an actual mass, so getting it wrong scales your entire tonnage error proportionally. The reference values in this tool are broad, typical ranges only, real in-situ bulk density differs from solid-rock SG through porosity, moisture, and voids, so a lab-measured value on your own ore is always better whenever you can get one.

4. What does setting a cutoff grade actually change in the result?

Any block whose grade falls below your cutoff gets reclassified as waste and dropped from the reserve, which usually lowers total tonnage but can raise the average grade of what’s left, since you’ve removed the weakest material. This tool shows both the filtered, ore-only figure and the unfiltered total together, so you can see exactly how much that one cutoff decision changed your reportable reserve.

5. Can I use this tool’s output for an official resource or reserve report?

No, this is a simplified, deterministic estimator meant for study and preliminary work only. Official reporting for investment purposes needs to follow a recognised industry code, like JORC, NI 43-101, or SAMREC, and needs proper geostatistical estimation along with sign-off from a qualified competent person, well beyond what a basic block-average tool like this one can provide.

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